Chelsea will take a narrow, yet precious, lead to Camp Nou. They played with exceptional levels of organisation, togetherness and structure and they can take great confidence from demonstrating that this brilliant, often mesmeric Barcelona side can be beaten, even if their opponents are too refined for Roberto Di Matteo's team to start thinking of themselves as favourites.
They won courtesy of Didier Drogba's breakaway goal at the end of a first half in which Barcelona had seemed in utter control. After that they had to endure another 45 minutes of almost unrelenting pressure. Pep Guardiola's side pinned them back at times. They hit the crossbar and saw chances cleared off the goalline. There was some exceptional goalkeeping from Petr Cech and, in the final moments of stoppage time, the substitute Pedro rolled a shot against a post.
Barcelona did everything, in fact, but score. Chelsea survived through strenuous effort, concentration and some good old-fashioned luck and, by the end, Lionel Messi could be seen screaming to the skies in frustration.
The jubilation at the final whistle was understandable given this was only Barcelona's third defeat this season. Yet enough was seen here, too, to show that they will still confidently expect to turn the tie upside down in Catalonia next Tuesday. If Chelsea are to complete the job and secure a date at the Allianz Arena, Munich, on 19 May, it is going to require an immense performance.
For long spells Barcelona kept the ball and exerted a sense of clear superiority. Yet they will reflect on their own carelessness, too, on a rain-soaked night when it was difficult at times to keep count of the number of chances they created. Cesc Fábregas and Alexis Sánchez, in particular, spared Chelsea with the generosity of their finishing.
At times Chelsea seemed to be gasping for air, symbolised by the frequency with which Drogba went to ground, signalling that he was hurt. It can be a tiresome habit but it did at least disrupt the flow of the game and, in doing so, disrupt Barça's momentum.
For all their dominance, the sporadic brilliance of Messi et al, it was not a night when Barcelona touched their most exhilarating heights.
This was not the masterclass we saw against Manchester United in last season's final and, for a team whose philosophy is that giving the ball away is a sin, they will not enjoy recalling the game's decisive moment.
The guilty man was, of all people, Messi. Frank Lampard dispossessed him just inside the Chelsea half and immediately looked to send Ramires running clear on the inside-left channel and, from that moment, Barcelona were in trouble. Ramires took the ball on his chest, advanced towards the penalty area and turned the ball into the centre. Drogba partially scuffed his shot but it was enough to beat Victor Valdés.
It was virtually the final kick of the first half and, as the players headed to the tunnel, Messi still shaking his head, it felt almost like a trick of the imagination that Chelsea were ahead. The first shudder of apprehension in the home stands arrived after nine minutes when Andrés Iniesta sent Sánchez running clear and the Chilean lifted his shot over the oncoming Cech only for it to come back off the crossbar.
Soon afterwards Messi set off on his first slalom through the Chelsea defence, beat a couple of men and played the ball into Iniesta's path. His shot was parried by Cech and Chelsea escaped only because Fábregas could not get a clean contact on the follow-up. The tone was set for a night when Barcelona were often playing with a 4-2-4 formation. Guardiola must feel his team had enough chances in the first 45 minutes alone to have killed the tie.
Chelsea's tactics were far less refined, looking to pick out Drogba, often playing alone in attack, and then relying on his muscular presence to hold up the ball. When he was not putting in a performance that Morgan Freeman would have been proud of, Drogba was a constant menace to the Barcelona defence. Di Matteo has got most things right since taking over from André Villas-Boas and the decision to play Drogba instead of Fernando Torres was spot on.
There were times, all the same, when Barcelona played with suave brilliance. Yet there were moments, equally, when Chelsea's opponents did not look as if they were enjoying themselves. Sánchez, once again, let Chelsea off, turning a 56th-minute shot past the post. Inferior as Chelsea were, there was some supreme defending at times, most notably Ashley Cole's goal-line clearance to keep out Fábregas and the countless blocks and interceptions from John Terry and Gary Cahill.
There was also Cech to save them with the outstanding save of the match, keeping out Carles Puyol's glancing header with only three minutes to go.
Even then there was more drama as Pedro hit the post and Sergio Busquets turned the rebound over the crossbar.
It was a brilliant night for Chelsea, yet one that also demonstrated what an immense performance they will need in Catalonia next Tuesday.