Here we are then A defining point in the 2010-11 season, or just another pointless cup fixture? I'm inclined towards the former, partly because I'm just not sure I'm feeling the same FA Cup ennui these days that some others are, but also because in this case there is some rather direct precedent.

In February 2008 Arsenal were top of the league by five points when they travelled to Old Trafford to face Manchester United in the FA Cup fifth round. Arsène Wenger put out a weakened side and found himself on the wrong side of a 4-0 hiding. The impact would go beyond a cup exit. Arsenal promptly went five league games without a win as their title challenge came off the rails.

If that wasn't a big enough incentive to take this game seriously then Arsenal will draw added motivation from more recent events. In the space of a fortnight they have lost a cup final and been on the receiving end of an absolute chasing from Barcelona at the Camp Nou (questionable refereeing decisions aside). To exit a third tournament so soon afterwards could prove a decisive blow to an already fragile state of mind.

United may be feeling vulnerable too, however, after consecutive league defeats away to Chelsea and Liverpool. A third loss at such a pivotal stage of the season would be very hard to stomach.

Team news There may be no question of either manager fielding a weakened side by choice today, but both are certainly constrained by injuries. United's line-up contains no less than seven players who would be most at home in defence - Brown, Smalling, Vidic, Evra, O'Shea and the two Da Silvas - but we're betting against a revolutionary 7-1-2. Arsenal start Almunia, their only fit first team goalkeeper, and are also without Alex Song, Theo Walcott, Thomas Vermaelen and ... some chap named Fábregas.

Man Utd: Van der Sar, Brown, Smalling, Vidic, Evra, Rafael Da Silva, Gibson, O'Shea, Fabio Da Silva, Rooney, Hernandez. Subs: Kuszczak, Berbatov, Giggs, Scholes, Valencia, Obertan, King.

Arsenal: Almunia, Sagna, Koscielny, Djourou, Gibbs, Denilson, Diaby, Wilshere, Arshavin, van Persie, Nasri. Subs: Shea, Rosicky, Ramsey, Squillaci, Clichy, Eboue, Chamakh.

Referee: Chris Foy (Merseyside)

In defence of United's team selection My colleague Jacob Steinberg just posted this on Twitter: "Actually, this United side is quite reminiscent of how Liverpool played against Chelsea." Not an unreasonable point.

How that United team will play Sir Alex Ferguson suggested to ITV that it will be a 4-4-2 with United, saying that Gibson would be partnered by O'Shea in midfield, with the two Da Silvas out wide.

If Arsène was a superhero "Mad props to the ITV people for using a bit of Hans Zimmer's fabulous Inception soundtrack," says Ryan Dunne, making reference to the British broadcaster's pre-game montage. "Although referring to Lord Ferg as the 'Dark Knight', as they just did, is plainly disturbing for any Batman fan. Does that make Arsène The Joker?"

1 min We're off, with United dominating the first 50 seconds's worth of possession, before Rafael Da Silva attempts to play in Hernandez. Only problem is he's comfortably offside.

3 mins And now a first shot for Arsenal, albeit a rather feeble one. Arshavin made Wes Brown look very silly indeed as he danced straight past the defender's sliding challenge with absurd ease, but Smalling was across swiftly to close the Russian down and ensure that he could only prod the ball gently at Van der Sar.

5 mins A section of the United fans begin that charming little libellous ditty they enjoy singing at Wenger, but another section almost immediately start up a chant of "United! United!" to drown them out. Signs of progress?

6 mins Samir Nasri jinks into space down the right hand side before whisking a cross over the area and over the head of Robin van Persie. Arsenal have been the more threatening side so far, though it may be a tiny bit early to start drawing sweeping conclusions.

8 mins Wilshere works the ball out to Gibbs on the left and he swings in a cross that is far too close to Van der Sar. The keeper claims easily enough. Interesting to see how Gibbs does in a game like this. Clichy is not the most popular player among Arsenal fans and with his contract negotiations at a standstill could be on his way out in the not too distant future. My own impression of Gibbs is that he is the more accomplished attacking player by far, but perhaps that some have overestimated the quality of his defending..

10 mins Nasri gets himself into trouble down by his own corner flag, eventually giving the ball away under heavy pressure from Evra. The ball is swung in by United towards Rooney at the far post but Arsenal cut it out.

11 mins Are you watching Cesc? Wilshere demonstrates the more reasonable part of the pitch in which to execute a backheel, rolling the ball under his boot to Arshavin as he runs at the United area. The Russian drives a low shot just wide of the near post, though it probably wouldn't have had enough pace on it it to trouble Van der Sar in any case.

12 mins "Surely Alex Ferguson would be Daredevil for the obvious reason," announces Anish Mistry. "Though considering Wenger's inability to see certain decisions he could certainly pass for him too." As one who has no idea who this Daredevil character is, I cannot really comment.

14 mins United seem somewhat unsure of themselves in possession at the moment. Perhaps understandably given the number of defensive players in the side, there doesn't seem to be a great deal of vision when they are looking to break forwards. Instead they roll it back and forth without advancing. Arsenal stand off, waiting for their turn to have it back.

15 mins Not for the first time, I seem to have spoken to soon. All of a sudden United create their first attack of note, Gibson feeding Fabio Da Silva down the left and the Brazilian whipping over a perfect cross that his twin can only head over the bar from a position right in front of the goal and a few yards out. That should have been a goal.

17 mins"Wenger has "Robin" on his side, how can he possibly be the Joker then," demands Brenda Wang on Twitter. It's a fair point.

19 mins Arsenal, by contrast with United are looking to attack quickly when they do have the ball, Nasri and Diaby exchanging passes down the right before an attempted cut-back for Van Persie is intercepted by Smalling.

21 mins Arshavin attempts to break across half-way but a heavy touch takes the ball away from him. United try to break but a similarly ragged piece of control from Hernandez allows the ball to run through to Almunia. Safe to say neither of these teams is playing quite at the peak of their abilities right now.

23 mins Arsenal are probing - not in the way that your Roswell-dwelling cousin says the extra terrestrial did, mind - around the edge of the United area but Sagna's cross is too deep. I suppose this is the obvious result of playing a team with this many defenders - easy to dominate in the middle of the park, hard to break down at the back.

24 mins Van Persie grows tired of the dawdling, looks up from a few yards outside the box and has a crack, his effort hit decently enough but ultimately travelling slowly enough and close enough to Van der Sar that the goalkeeper is able to gather it at the first attempt.

26 mins The game is settling into a pattern now, with Arsenal holding a lot of the possession in the United half and their hosts playing on the counter. Rafael Da Silva sends a ball over the defence down the right for Rooney to chase, but he's put too much on it and it runs out for a goal-kick.

GOAL! Manchester United 1-0 Arsenal (Fabio Da Silva 28 mins) Who needs attackers? Fabio Da Silva is on hand to gobble up the rebound after Hernandez's header is palmed away by Almunia. The goalkeeper will be livid that both players were so easily able to get in behind the Arsenal defence, but the header was excellent - right across the goalkeeper so that even if he did reach it he would have little choice but to push it out into the middle of his own area.

30 mins Now United have the momentum with them and Rooney manages to pick out Fabio Da Silva again inside the box with a very tidy cross, but the Brazilian's gets the header all wrong and Arsenal clear.

32 mins "Were Rafael and Fabio separated at birth," sniggers Ian Copestake. The evidence here would suggest they were kept together, Ian.

33 mins Ooh - best effort of the game by far for Arsenal there as Nasri manages to create just half-a-yard of space for Van Persie with a clever ball as he moves out towards the touchline from the centre of the D. The Dutchman turns and fizzes a low shot across Van der Sar's goal and his shot might just be sneaking in before the goalkeeper gets a hand to it and pushes it away for a corner ... From which Van Persie crashes a header just wide at the near post. Perhaps should do better with that.

35 mins Rooney just sent Sagna clattering into the advertising hoardings with a foreceful but fair challenge on the left.

36 mins Apologies, I'm hearing from some readers that my descriptions of the goals are not showing up. This seems to be due to a flaw in our auto-update system. If you could just refresh your page manually now they should appear. From now on I'll try a work-around to make sure the description shows up.

38 mins "Here's a useless stat - Ryan Giggs joined United on the birthdate of the Da Silva twins- 9 July 1990," parps Nick McLoughlin. "Does that make him feel old or them feel young?" I think that makes us all feel old, Nick.

39 mins Not the response Wenger will have been hoping for so far here at Old Trafford. Another move comes to an end with a disappointing piece of miscontrol from Nasri and since the goal there really hasn't been any sort of concerted reaction. With seven defenders on the pitch the first goal was always going to be important but a team with such faith in their attacking abilities as Arsenal would surely expect to be able to do more than they are at the moment.

41 mins Fabio pulls an exemplary 'I can't believe such an injustice. On a football pitch of all places' face after the referee declines to award him a free-kick following a tussle from Denilson. Crucial part of any pro's skillset, that.

43 mins Smalling, who is having a pretty tidy start to this game, dispossesses Arshavin again on the edge of the area, before tearing up the field to within about five yards of the Arsenal area. Then he realises where he is, passes the ball sideways and starts running backwards with a fury. The ball is worked through to Rafael but he is muscled off the ball by Djourou.

44 mins "Would three cup exits in a fortnight set a record," ponders Nick McLoughlin. That's one for The Knowledge, I suspect.

45 mins Nasri, not for the first time this season playing the part of Arsenal's most significant attacking threat, sells Wes Brown a dummy pass across the area before twisting back to thrash the ball through his legs and towards the near corner of the net. Van der Sar does very well to get down quickly and smother the shot..

Peepety-peeeep! Half-time at Old Trafford and despite having all those defenders on the pitch it is United who once again lead against Arsenal. The Gunners have had a lot of the ball in good areas of the pitch but threatened to get back on terms only very sporadically after Fabio's opener. A lot more will be required if they are to get back into this in the second half. Back in a tick with half-time emails.

On the subject of Wenger as Daredevil "Great point by Anish Mistry (12 mins)," says Ryan Dunne. "Daredevil is a blind superhero whose other senses are other superheroically enchanced. Daredevil literally never sees the incident, hence Wenger, but the 'red devil' outfit is a bit Fred the Red, and the comics' grim-in-gritty Hell's Kitchen setting arguably is more suggestive of Lord Ferg's Govan origins."

On the subject of Arsenal's transfer policy "Am I alone amongst Gooners in thinking that if Arsène could once, just once, do something disreputable in the transfer market - signing Kevin Nolan for instance - the script of matches like this might be somewhat less predictable," muses Allan Castle. "Seeing Evra with his collar up in the tunnel made me wonder who in the Arsenal XI was capable of administering an attitude adjusting tackle."

On the premature anointing of Kieran Gibbs "Is Gibbs really being pencilled in as an England full-back for the next 10 years," demands David Wall. "Really? Has no one learned from Glen Johnson?"

And finally ... Arsenal as an impotent boyfriend "Arsenal are a frustrating boyfriend - smart, talented, beautiful, also plenty of intricate action in and around the box," asserts Linda Howard. "Yes, the lack of penetration is frustrating but ultimately all the other aspects make it all worth it."

46 mins "Do you think Valencia will play today," asks Jorge Narvaez. "And if so do you think he will have a big impact in the game?" Well, he's just been introduced at half-time in place of the goalscorer himself Fabio Da Silva, so we're about to find out. We're off again and Wenger is trudging over to his bench with a less than exuberant grimace on his face.

47 mins Wilshere comes cantering forward, eluding a pair of challenges and then bouncing off another - Arsenal might well have got a free-kick right on the edge of the box had he chosen to go down - but in the end can only scuff a gently effort goalwards.

48 mins Fantastic save from Van der Sar - and what a bizarre goal it would have been too. Heaven knows what Laurent Koscielny was doing that high up the pitch, but suddenly the Arsenal centre-back found himself in yards of space inside the United area. Presumably confused by this himself, he initially attempts to square the ball to Van Persie, but when the ball comes back to him off a defender he finally shoots from five yards out and the keeper has to show incredible reflexes to push his shot away at full stretch.

GOAL! Arsenal 0-2 Manchester United (Rooney 49 mins) Just when it looked like Arsenal were making a bright start to this half they concede again. Djourou had done exceptionally well to block Hernandez's effort five yards out after a centre from Rafael, but the ball bounced up into the air and Rooney directed his header with supreme confidence past Almunia and into the net from a really quite acute angle. Game over?

51 mins Arsenal, understandably, seem rocked by that second goal and it looks for a second as though United are about to add a third as Rooney plays Hernandez in down the left with well-judged throughball, only for the flag to go up for offside. It was the right decision, but not by much.

53 mins "Can we do footballers named after cities clashing on the field," asks Nick McLoughlin. "We have Valencia vs Abu Dhabi here after that half-time change."

54 mins United are letting Arsenal have the ball now, but only in areas where they aren't going to do any harm. There is an air of frantic hopelessness about Arsenal as they move the ball around with great urgency but very little direction in the middle of the field.

56 mins What an intervention that was from Vidic - reaching out a size 11 at full stretch to cut out a chip forward from Arshavin that seemed certain to end up at the feet of Wilshere as he ran free towards the United goal. Smalling has been impressive today but it makes such a difference having Vidic alongside him.

57 mins Nasri tests Van der Sar again with a half-volley flashed towards the roof of the net from just inside the area after United fail to clear an attack, but once again the effort hasn't quite got enough power behind it and the goalkeeper claims it first time.

59 mins Diaby sums up his contribution this afternoon by clunking a shot a long way high and wide from a position 25 yards out where passing might have been the better option. A luxury player in a team who may already have one too many. Arsenal are sending Marouane Chamakh on for Denilson.

61 mins Arsenal win a free-kick in a useful spot a yard or two outside the D after Van Persie is felled by O'Shea. No prizes for guessing who is going to take it ...

62 mins Van Persie's free-kick hits a United player (I want to say Gibson, but without a replay I'm not sure) flush in the face, but the fact that the man in question barely seems to flinch tells you everything about the lack of pace in the shot. The Dutchman was clearly attempting to go with precision rather than power, but wound up with neither.

64 mins Time for another United change. Ryan Giggs replaces the second Da Silva twin.

65 mins "In response to Nick McLoughlin (53 mins), it's such an old Clichy to make jokes about players names," chirrups Jimmy Lacey as United waste a corner. "Mind you, with this carnival football that United are playing, it's as if they think they're in Rio. Nemanja what I mean?" I was with you right up to Nemanja.

66 mins So close to a third for United, as Chris Smalling finds an unmarked Giggs with a header across the six yard box from the back post but the Welshman just can't get the ball to come down fast enough as he tries to bring it down on his chest. Djourou recovers to clear.

67 mins At the other end Chamakh forces a save out of Van der Sar with a low drive after coming in from the left, but it will require a lot better effort than that to beat the keeper on this sort of form.

69 mins "Giggs, Giggs will tear you apart again," crow the United support. Arsenal's players look increasingly forlorn - shoulders slumped and energy draining from them as the minutes tick away. Still 20 minutes to play but it's hard to see a way back right now.

72 mins Arsenal make their second change, introducing Aaron Ramsey for his first appearance since his horrific injury last year. He replaces Abou Diaby. In fact they're going to make their third one too, Tomas Rosicky replacing Andrei Arshavin.

73 mins Nasri attempts to thread the needle with a pass through the middle for Van Persie, but if he had waited a fraction of a second longer he might have seen Ramsey tearing up alongside him and into far more space on his outside shoulder. The Welshman has a decent shot on him, too.

75 mins Not for the first time, Wilshere has probably been Arsenal's best player today, and he prises open the United defence as best he can here, beating one man and eluding the challenge of another by releasing the ball to a team-mate just behind him. He then steps past the defender to take the return ball inside the box but then crashes his shot wide of the near post.

76 mins Another chance goes begging for Arsenal - Chamakh heading down into the ground and watching the ball bounce up to a spot where Van der Sar can palm away after Sagna had found him with a wonderful cross from the right. It was another decent save by the keeper, but from the position where he received the ball the striker should have made him work far harder than that.

78 mins Yet another save required from Van der Sar (and for all United have managed this game well, you could certainly make a case for him as the man of the match) as Rosicky lets fly at the top corner from the edge of the box. The keeper can only parry back out towards the penlaty spot but the ball falls closer to Smalling than Chamakh and the striker fouls his opponent as he strives to recover possession.

80 mins A fantastic counter-attack from United and a fantastic save from Almunia to deny them at the end of it. Giggs cuts inside as he races forward, nudging the ball to Rooney as they cross paths. He squares the ball to Hernandez six yards out, but his attempt to bundle the ball home takes a deflection off Djourou before ricocheting up and oh so nearly over Almunia, who had already gone to ground - but the keeper thrusts out a paw to palm the ball away.

82 mins Things going from bad to worse for Arsenal here - Djourou is still down and receiving treatment from what looks like about six men at the moment. The stretcher team are waiting to carry him off, but the medics aren't ready to hand him vover just yet. In the meantime, United have taken off Patrice Evra and brought on Paul Scholes.

84 mins Djourou still receiving treatment. What a blow this could be for Arsenal. The defender is yet to lose a Premier League game this season.

85 mins "Cork Vs Dublin must surely have happened in early days of the Premier League," announces Ronan by email, returning to our cities facing off on the football pitch theme. "It is the ultimate battle of cities over here in the motherland of manchester utd's central midfielders."

86 mins Djourou finally leaves the pitch on a stretcher, and the suspicion is that he has dislocated his shoulder, which I can say from experience is not a fun place to be.

88 mins Rooney, who has been quietly brilliant this afternoon, feeds Hernandez down the left with a neat blind pass but his team-mate's cross is overhit and runs away on the far side of the area.

89 mins Gibbs sums up the seemingly hopeless position Arsenal find themselves in, picking the ball up in a potentially threatening position just inside the left-hand corner of the area but freezing completely for a second before thwacking the ball aimlessly into the nearest opponent's thigh.

90 mins We are going to have a good eight minutes of injury time. Which is actually probably about right after that Djourou injury. Not that's it's going to make much difference to the outcome of this game.

90 mins (+2) Arsenal may be looking lifeless but if nothing else there fans remain in fine voice - making themselves heard far more than the home support in these closing stages.

90 mins (+3) I dare say he'll be forgiven after his performance in the rest of this game, but Rooney makes a horrendous mess of an absolute gem of a chance - slicing his shot wide from about five yards out.

90 mins (+4) Quite the unnecessary challenge from Scholes there - crashing in two-footed on Chamakh inside the Arsenal half. He took the ball but that's a dangerous challenge at the best of times and really quite needless at this stage of a game like this.

90 mins (+5) Another chance for Arsenal - and they've had their fair share in the end, even if they haven't scored - Sagna picking out an unmarked Rosicky right by the goal but the midfielder failing to trap the ball and letting it get away from him.

90 mins (+6) My word, what is Scholes at here? Another two-footed challenge earns him a talking to from the ref but honestly, what is the point in that?

90 mins (+8) And if Arsenal really could have scored today then United certainly could have had a third too. Almunia again manages to deny Hernandez from close range.

Peep! Peep! Peeeeeeep! That's it from Old Trafford - Arsenal exit a third cup competition in the space of a fortnight. The mooted quadruple is now down to a single, and though both players and fans would clearly be delighted to end their season with 'just' a Premier League title it is increasingly hard to imagine this team picking itself up from a run like this to chase down United in the league, especially after losing as important a player as Djourou had become over the last few months. As for United, yet again under Ferguson they have managed to put on a show of strength at a time of adversity. That ITV should indeed name Van der Sar as Man of the Match in the end makes it clear that Arsenal threatened to score at times, but despite the number and calibre of the players they had missing, United still deserved this win. They will draw confidence from another big victory when they needed it most. Right, that's it from me. Thanks for all your emails and sorry I couldn't use more of them.