Full time: Barcelona 4-0 Milan (4-2 on aggregate)

There's the final whistle and Barcelona are into the quarter-final, becoming the first side to overturn a 2-0 first-leg deficit in the Champions League! It was 4-0 to Milan in the final in 1994 and it's 4-0 to Barcelona tonight after a truly exhilarating performance from a side who have answered a few questions from their critics tonight. At times they were out of this world, particularly the two goals from Lionel Messi that calmed the nerves in the first half, and the third goal from David Villa was wonderful. Look at that, Villa in, Fabregas out, and Barcelona tear a good side apart. Milan will wonder what might have been, especially given the chances that Niang and Robinho failed to take, but ultimately they were outclassed. Thanks for reading and emailing. Over to Arsenal now.

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90 min+3: There's still time for Mexes's shot from the edge of the area to drift wide, and...

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GOAL! Barcelona 4-0 Milan (4-2 agg; Alba 90 min+2)

Jordi Alba, whose tackle denied Robinho a certain goal a few minutes ago, seals it for Barcelona! It all came from a Milan free-kick, which for reasons best known to Robinho wasn't hoisted into the Barcelona area, even though all the big men had trotted forward. Instead he took it short and, inevitably, Milan lost the ball. Messi released Sanchez down the right, he did something right for once by clipping the ball across for Alba - the left-back for God's sake! - and he dinked it past Abbiati.

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90 min: There will be three more minutes of whistling.

89 min: Barcelona have a corner. They're in no hurry to take it and Milan have the funk on.

87 min: The tension is unbearable. Bojan's shot from the right takes a deflection and bobbles around the area but the flag goes up for offside. It wasn't clear who was offside.

86 min: Ouch, my ears. The whistles are deafening as Milan start to turn the screw. I suppose I could just turn the volume down.

84 min: Barcelona make their final change, bringing Adriano on for Pedro.

83 min: I should point out that Robinho's chance wasn't quite as good as the one Nicklas Bendtner missed for Arsenal two years ago, simply because of Alba's defending.

82 min: I'm not sure if Barcelona have it in them to hold on to this. On the left, Bojan runs at Pique and easily beats him before sliding a low cross into the six-yard box, where Robinho looks certain to score, only for Alba to deny him with a last-ditch tackle! What a chance! What a tackle!

80 min: Into the final 10 minutes we go. Barcelona are in control but it will only take one slip for Milan to go through. Suddenly Milan find themselves in a promising position around the Barcelona area but Muntari's charge from Robinho's pass is firmly halted by Puyol.

78 min: Alexis Sanchez has the ball in the net after rounding Abbiati but he was inches offside as he ran on to Pedro's pass. Constant got away with that.

77 min: Xavi plays a pass inside Abate for Alba, but the Milan right-back recovers to concede a corner. Before the corner can be taken, Carlos Puyol replaces Javier Mascherano. "Abate just never stops," says Ian Copestake. Indeed if Milan score it will probably come from one of his raids.

75 min: Milan also replace Mathieu Flamini with Bojan, a former Barcelona striker. Bojan, of course, had a stoppage-time winner ruled out for a Yaya Toure handball when Barcelona lost to Inter in the semi-final in 2010.

74 min: Messi drives his effort straight into the wall and that's the cue for Barcelona to replace David Villa with Alexis Sanchez.

73 min: Messi tries to wriggle clear of Zapata, who clips his heel. A free-kick to Barcelona around 25 yards from goal and it's made for Messi's left foot.

71 min: "Milan are still favorites, I say," says Jack Goodson. "Pippo Inzaghi to lurch onto the field in the 89th, tap one in two minutes later and then run into Gary Neville's waiting arms."

70 min: It's now Schalke 2-2 Galatasaray, who lead on away goals.

68 min: Abate gets forward again and Barcelona make a mess of clearing his cross. The ball falls to Boateng, who drills a low cross-shot into the area. Flamini tries to flick it in, but in the end the referee awards a free-kick to Barcelona.

67 min: The nerves when Milan go forward are palpable. Barcelona need to score again.

66 min: Abate motors forward, at such a pelt he outpaces Alba, and his excellent cross would have been a better idea if a Milan striker was in the area.

65 min: "Clearly Milan have realised that a Portsmouth FA Cup runner up isn't enough, and have sent for an FA Cup winner to get them back in the tie," says Matthew Loten. "If only they had Milan Baros on the bench instead of Robinho, they'd be a shoe in for the next round."

What's Kanu up to?

63 min: Messi chuckles after being fouled by Muntari. It appears to be the only answer Milan have for him.

62 min: A clearance is chested up by Messi on the edge of the area and his instant volley flies just over. He's been absurd.

60 min: Massimo Ambrosini is replaced by Robinho and Sulley Muntari is on for Niang as well.

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59 min: "I think your commentary is biased towards Barcelona," says Utsav Nagwan. True, especially as they're losing 3-0.

57 min: You still wouldn't back Barcelona to keep a clean sheet. I think they'll need another.

GOAL! Barcelona 3-0 Milan (3-2 agg; Villa, 55 min)

David Villa vindicates the decision to include him with a lovely finish and Barcelona are ahead in the tie for the first time. Now Milan have to score. You always felt they couldn't keep giving the ball away in their own half and this time they've been punished to the fullest degree. Mascherano stepped in to win a Milan clearance, knocking it to Iniesta, who lays the ball off to Xavi. He spots Villa on the edge of the area and once Constant commits himself, the striker is through. His first touch is excellent, allowing him to open up his body and bend a fine left-footed finish into the far corner. Abbiati stood and watched.

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54 min: Mexes becomes the latest player to be booked after taking out Messi on the right touchline. He'll miss the next match if Milan go through. Milan are refusing to let Messi get into his stride with their rotational fouling.

53 min: Niang's corner finds Boateng, who hits a difficult volley high and wide.

52 min: Milan are starting to play a bit and Niang, in space on the right, wins a corner off Alba.

51 min: Messi turns a pass round the corner for Villa, but his return flick falls short of Messi. Villa, as I keep saying, has been relatively quiet but his movement is giving Milan so much more to think about.

49 min: Milan have pushed up. Armed with the knowledge that they're going to need to score now, they're determined to press Barcelona much harder now. Problem being that Barcelona might just pass it round them.

48 min: Constant gives the ball to Messi inside his own half. Just what you want to be doing. He glides past Mexes and makes his way past Zapata too, but doesn't catch his left-footed shot well enough and Abbiati saves comfortably enough.

46 min: Off we go again, Barcelona kicking off and attacking from right to left. Allow me a prediction: either way, this isn't going to extra-time. "Referee is having a somewhat cowardly match but Dani Alves' crossing is awful," says Gene Salorio. "Barca might just as well put the ball out of play as give it to him in an advanced position on the right."

Messi's goals: The first was delicious, placed in between the tiniest of gaps left by Mexes and Zapata before floating into the top corner in slow motion. The second? He was miles offside when Iniesta passed to him.

In the other game, it's Schalke 1-2 Galatasary at half time and 3-2 on aggregate to the Turks. What a turnaround there. They fell behind to a goal from Roman Neustadter after 17 minutes, but goals from Hamit Altintop and Burak Yilmaz have put them in front.

Maybe the reason Niang missed that chance was because Gary Neville wasn't there to offer a goalgasm.

Half time: Barcelona 2-0 Milan (2-2 aggregate)

Barcelona took 39 minutes to wipe out Milan's lead thanks to two stunning goals from the stunning Lionel Messi. All logic suggests they should go on to win this match but that chance for Niang shows how quickly momentum can turn.

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45 min+1: There will be one added minute and it's Milan who are on the attack. And then it's Barcelona who are on the attack, so Flamini scythes through Pedro, earning a booking that earns him a suspension.

45 min: You won't be surprised to learn that Barcelona want a third that would put them ahead on aggregate. Milan need half-time.

43 min: What drama and there's more to come. That is all.

41 min: Pedro is booked for a foul on Abate and will be suspended for Barcelona's next match.

GOAL! Barcelona 2-0 Milan (2-2 agg; Messi, 39 min)

This is how crucial that Niang miss was and Barcelona are now level on aggregate. Messi hadn't scored against an Italian side in open play before tonight and now look, he's got two in one half. Ambrosini lost possession to Iniesta in his own half, like Cesc Fabregas in March 2011, and he instantly found Messi on the edge of the area. He shifted it on to that deadly left foot and his low drive into the bottom-right corner was past Abbiati before he'd had time to think about it.

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38 min: Milan hit the post! Incredible! It was a moment that summed up Barcelona's defensive failings, as Mascherano dealt with an aimless long ball in awful style, heading it straight to Niang, who was suddenly in the clear. The Nou Camp fell silent as he sprinted away into Fernando Torres territory but he almost had too much time to make his mind and his low shot beat Valdes but not the left post. How crucial could that be? This crucial...

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36 min: As a Portsmouth fan, looking at the caption under the header image has left me feeling quite offended by your choice of words," says Matthew Loten. "I'll have you know Boateng didn't so much play for us as, along with Ricardo Rocha and Jamie O'Hara, drag an awful side to an FA Cup final. Just don't mention the missed penalty... I hope if Milan wins the CL this season he breaks out the moonwalk celebration again!"

Let's not forget the work of Uncle Avram.

34 min: Like this. At last El-Shaarawy is released on the left. He steps inside a challenge and into the area but can't beat Valdes with his attempted curler.

33 min: If Milan can stop knocking the ball out of play every time they get into a vaguely promising position, then there's space for them to exploit out there. As it is, they're too careless in possession.

32 min: Barcelona were absurd in the first 20 minutes but Milan have slightly weathered the storm in the last 10 minutes or so. They're also starting to look more threatening on the break.

30 min: Might I point out that the referee is letting Milan get away with a few challenges that might be deemed illegal and after Alba doesn't get a free-kick despite being clipped, Niang is released down the right. His deep cross finds El-Sharaawy, whose attempted overhead kick doesn't cause Barcelona any bother.

29 min: Now Flamini has had to change his shirt. I'm surprised the other Milan players haven't followed suit - they must be dripping.

27 min: The slightest of lulls. "Let me begin by saying I dig your new official Guardian photo - it looks a lot more mature and professional than the previous offering," says Dan Schulwolf. "Is this an attempt to move from the ranks of the football hipsters into the rarefied air of seasoned veterans such as Glendenning and Smyth? In any event, it seems like Barcelona is battering Milan at the moment. Unfortunately, I'll have to miss the inevitable sending off for Milan and the equally inevitable Barcelona collapse as I have to write an essay on the historical merits of Jonathan Spence's baffling The Death of Woman Wang. Final score: Barca 3-1 Milan."

To be fair, the previous photo was taken four years ago in a bar in New York.

25 min: Messi finds Xavi, who spots Alves on the overlap. His first-time cross is slightly misjudged though and Pedro heads well wide. On the touchline, Flamini is having his head bandaged.

24 min: David Villa hasn't done a lot but his presence alone seems to have afforded Messi more space, making the constant selection of Fabregas look even more ludicrous.

22 min: Kevin Prince-Boateng picks up the first booking of the night for a foul on Iniesta, while Schalke are 1-0 up against Galatasaray and lead 2-1 on aggregate. "Messi's body language would suggest he's still in a bit of a funk but he's got just enough energy to single handedly kick Milan's ass before heading back to the sofa to watch Season 3 of The Wire with a bag of crisps and some maté," says Matthew Carpenter-Arevalo.

21 min: Barcelona have a free-kick around 30 yards from goal, just to the left. Alves stands over it but Xavi takes it, trying to slip Pedro in Javier Zanetti-style. Montolivo reads it but there's no respite for Milan, Pedro going over in the area again. Another appeal is waved away.

20 min: "In response to Harry Tuttle's query about the most hipster match...in 4 hours there will be the quarter finals of the CONCAF Liga Champeons between Monterrey of Mexico and Xelaju of Guatemala," says David Grinter. "I'm not a hipster or anything, I just happen to be in Quetzaltenango in Guatemala at the moment. The score is 3-1 to Monterrey after the first leg if anyone cares..."

19 min: Pedro. Iniesta. Pedro... almost Iniesta again, but Abate hurriedly turns it behind for a corner. They're surely going to score again. There is absolutely no way Barcelona shouldn't get the right result tonight - they are so superior to Milan.

17 min: This is an outstanding save from Abbiati, who flies to his left to tip a swerving drive from 25 yards out from Xavi inches wide. I thought that was in. He got the merest of fingertips on that.

16 min: Niang wins a corner on the right for Milan. It's sent to the far post and almost falls for Zapata, the ball eventually looping into the hands of Valdes. Up the other end, Abate's woeful backpass almost gifts Villa a goal but Abbiati does enough to put him off! There's barely time to catch your breath.

15 min: With four Milan players around him, Messi appears to nutmeg all four of them at once. He is, it's fair to say, in the mood. "Am reliant utterly on your word pictures as my feeds from China and Romania just don't want to come out and play," says Ian Copestake. "Are you watching moving pictures in colour? That must be amazing."

13 min: What a save from Abbiati and what an escape for Milan, who are being given a chasing here! On the right, Alves swings a cross towards the far post where Messi of all people heads the ball down to the edge of the area to Iniesta. The ball bounces up invitingly for the volley and Iniesta's technique is perfect, compelling Abbiati to spring to his right and push the ball on to the bar! The rebound comes out to Messi and he can only head the ball into the side-netting. Barcelona are threatening to run away with this, although as it stands Milan are still going through.

11 min: Barcelona scream for a penalty as a ball over the top from Xavi finds Pedro, who is clattered from behind by Abate. Pedro goes down but the referee waves play on. If he'd given a penalty it surely would have been a red card, so he might have bottled that decision. Moments later, Milan hand the ball straight to Messi, who almost slips Iniesta in.

10 min: This is set up fascinatingly. Milan are giving Barcelona far too much room but equally that chance a minute ago shows that they can score. "That is just gooey loveliness from Messi," is Simon McMahon's verdict on the goal.

9 min: And here's the danger for Milan. A ball from the right flank from - I missed who - catches out both Pique and Alves, who fails to spot El-Sharaawy darting in behind him. His touch was too heavy though and took him away from goal, and his eventual shot was tamely at Valdes.

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7 min: That was truly brilliant. Messi is just absurd, isn't he. Feel free not to respond to that. The speed of the passing was breathtaking.

WHAT A GOAL! Barcelona 1-0 Milan (1-2 agg; Messi, 5 min)

One down, one to go and what a brilliant goal this is. We spoke before the match about Lionel Messi never having scored in open play against an Italian match but he's stored up a peach in his 10th match against one. Milan were already starting to breathe heavily as this Barcelona move got cooking. Astonishingly quick passing saw Messi pick up the ball in a pocket of space 20 yards out. There were around four or five Milan shirts crowded around him but Messi played a one-two with Xavi, shifted the ball on to his left foot and then curled a shot into the top-right corner from just inside the area. Abbiati didn't move.

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4 min: Boateng picks up the ball, just inside his own half on the right. He looks up and sees three Barcelona players around him so just pings it down the line to no one in particular. That could turn into a real problem for the Italians, who are already struggling to keep the ball. "As Barca's most famous season-ticket holder used to be John Paul II, perhaps it is not coincidental that their form has deserted them so miserably in a world without pope," says Justin Kavanagh. "Failing a miracle, I fear the forces of Berlusconi's evil will prevail tonight and leave ticki-tacki believers watching sulfurous black smoke rising from the Nou Camp tonight."

3 min: This is not news but Milan can hardly get a kick at the moment. "Can't stop wondering about the tables," says Phil Withall. "I mean were they being chucked into some sort of funeral pyre or balanced precariously like the tower of Pisa. This worry may well ruin my evening. I need answers!"

2 min: Barcelona seem to have started with three at the back - Mascherano, Pique and Alba. Messi appears to be playing from the right which is where he began his Barcelona career of course. Pedro is on the right and Villa is in the middle. It should be interesting to see how this pans out.

Peep! We're off and this should be good. Milan get us going from right to left, to ear-piercing whistles. They keep the ball for exactly seven seconds and it could be a while before they see it again. Not that they weren't expecting that. "Doesn't Lee Dixon look like Tin Tin?" says Tom Shaw, correctly.

The teams are in the tunnel. And now they're on the pitch. Barcelona are in blue tracksuits, Milan are in all white. I'd tell you what the atmosphere's like - the Barcelona fans are holding up a mosaic that reads "We are a team" in Catalan - but ITV have gone to another ad break. "What is so special about the end of Antonio Nocerino's beard?" parps Colum Farrelly. It's got magical powers. Didn't you know?

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Does anyone know where I can get some Gazprom? I really want some Gazprom.

Some more pre-match emails, seeing as ITV have waited four minutes before the first ad break.

"The IT department will be following your mbm today," says Tony Campisi in LA. "Present are Tony (Anyone But Barca), Rhett (Barca), Hunter (Barca) and Doug (Barca). Also, Emmerdale is not available in the States, to my knowledge. Sergio ruined Barca for me."

"Football just doesn't get tougher than this," says Simon McMahon. "I expect this match to deliver on every .. single .. level."

"A lot of people like to go on about Daniele De Rossi's beard being the best in the business," says Colin Sebastian. "That's a joke. Antonio Nocerino's. End of."

"Which is more hipster, Milan/Barca or Leicester/Cardiff?" says Harry Tuttle. There must be something going on in the Finnish Second Division?

"Notice how the Cardinals called it a day half an hour before AC Milan plays Barcelona," says Jerry Slaff. "Coincidence?" They had to get home in time for Emmerdale?

Non-football news story of the day.

"Just the thought of what might happen in this match tonight has really got my juices going," says Simon McMahon. Silence! I'm watching Emmerdale.

Right now I'm watching a top, top episode of Emmerdale. A man who appears to be Brian McDermott has just entered the room.

Teams

Barcelona see sense and drop Cesc Fabregas, meaning that David Villa is reunited with Lionel Messi and Pedro, instantly improving their chances of scoring the goals they require. Javier Mascherano plays instead of Carlos Puyol in defence. Milan are without the cup-tied Mario Balotelli and the injured Giampaolo Pazzini, while I had forgotten about the existence of Robinho. What price former Barcelona striker Bojan coming off the bench to score the winner?

Barcelona: Valdes; Dani Alves, Pique, Mascherano, Jordi Alba; Xavi, Busquets, Iniesta; Pedro, Messi, Villa. Subs: Pinto, Fabregas, Puyol, Sanchez, Adriano, Song, Tello.

Milan: Abbiati; Abate, Mexes, Zapata, Constant; Ambrosini; Montolivo, Flamini; Boateng; Niang, El Shaarawy. Subs: Amelia, De Sciglio, Muntari, Robinho, Nocerino, Bojan, Bonera.

Referee: Viktor Kassai (Hungary)

Preamble

Good evening. Tonight we come to bury Barcelona, to demand that Lionel Messi hands back his Ballon d'Or and to agree with that infamous Daily Mail headline about Xavi Hernandez. Lose for the fourth time in six matches, lose after losing twice to Real Madrid, lose again to Milan – well, Barcelona will be finished and tiki-taka will be a busted flush. Lose tonight and it will be Barcelona's earliest exit in the Champions League since Liverpool beat them in the last 16 in 2007. In the years since, they have won the tournament twice and have reached the semi-finals on three other occasions. Lose tonight and the feeling of decline will be unmistakable.

Or so the narrative has it and let's be careful not to get too far ahead of ourselves. Sometimes in football it is easy to get too excited, to write sides off and to forget that this is Barcelona, that they have Andres Iniesta, Xavi and Messi, that they are 13 points clear at the top of La Liga. If they do get into their stride and score early, they could do bad things to Milan, unspeakable things, and then we'll be wondering what the fuss was all about. Funny how the machine works.

The problem, mind you, is that they haven't hit their stride for a while. The 2-0 win over Deportivo on Saturday was their first clean sheet they have kept in two months and one goal for Milan would leave Barcelona needing to score four to go through. The way their attack has been playing lately, you wouldn't bet on them pulling that off. Both Real and Milan have made them look predictable, one-paced and overly reliant on Messi, a consequence of the inexplicable fiddling with the midfield of Busquets-Xavi-Iniesta, the failure to improve the front three adequately and, grubby as it feels to mention it, the emotional toll caused by Tito Vilanova's illness. It is unfair to criticise Jordi Roura, doing a job he never asked for in extremely difficult circumstances, but he has appeared unable to make the necessary in-game changes to get Barcelona out of trouble.

Unlike against Chelsea last season, they failed to create a chance of note in the first leg against Milan, although the Italians should of course receive a huge amount of credit for a brilliant gameplan that was implemented perfectly. They did not park the bus but squeezed the middle, forcing Barcelona wide, pressed feverishly and then took their chances with considerable aplomb. Few would have expected this when Milan were struggling in the first half of the season but they are starting to look like a proper side. We'll learn a lot about them in what should be the ultimate test this evening. Sure, they'll have to defend for what will feel like an eternity but they have the forwards to take advantage of any loss of focus in the Barcelona defence, have scored three times in two matches at the Nou Camp and know that Messi has never scored in open play against an Italian side.

Much has been made of Milan's collapses from seemingly impregnable positions - the defeat to Deportivo in 2004, the Miracle of Istanbul, the escapes against PSV Eindhoven and Arsenal - although this Barcelona side are not great at chasing games. History, it would appear, is arguably against both sides - what might be decisive is Barcelona are against Milan. Although it's not entirely clear who that's meant to favour.

Kick-off: 7.45pm

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