Barcelona have to win on Tuesday. If the Catalans are to progress to next month's Champions League final in Munich, they will need to overturn a one-goal deficit from the first leg in London last week. And with the Blues set to repeat their Stamford Bridge strategy of defending in numbers and attacking on the break, Barca look to be in for a tough test.
Coach Pep Guardiola was left frustrated following the defeat in London and then saw his side lose the Clasico to Real Madrid at Camp Nou on Saturday. And with their hopes of winning La Liga now seemingly in tatters, the Barca boss must ensure the same thing does not occur in Europe.
Take a look at what Guardiola could do on Tuesday to ensure his side progress to the final and a possible meeting with either Madrid or Bayern Munich.
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With Chelsea defending bravely and the midfield packed with men last week, Barca needed to look to the flanks but failed to do damage on the wings as Dani Alves and Adriano were unable to get beyond the Chelsea full-backs and assist the forwards.
Alexis Sanchez and Lionel Messi looked to attack through the middle and were faced with a wall of defenders, while Xavi and Cesc Fabregas were unable to take advantage of the pockets of space left by a rigid rearguard to open up the game with delicate through passes, either.
With little space to advance, Barca did try their luck from distance but saw the majority of their efforts blocked as Chelsea's defenders threw themselves heroically to stop the ball. Adriano and Seydou Keita both shoot well from distance, while Xavi, Messi and Andres Iniesta can also strike from long range.
Barca must use both of these resources on Tuesday.
A MORE CONVENTIONAL FRONT THREE
In the first leg, Alexis Sanchez made a number of diagonal runs into the middle when he received the ball. And although he took up two excellent positions from which he should have scored, he also came up against an almost impenetrable back line. In the Clasico, Pep was criticised for his use of Cristian Tello in attack, but the idea in theory was a good one and a more conventional front three could have done more damage in London, where Fabregas was utilised in a deeper role. Stretching the play with two fast forwards on the flanks and creating more space for Messi in the false-nine role could cause Chelsea problems in the return.
MAKE PROACTIVE CHANGES
With no space in midfield and few openings for Barca, changes were needed at Stamford Bridge. Guardiola was more reactive than proactive as he sent on Pedro for the injured Alexis Sanchez after 66 minutes, while Thiago replaced Cesc with 12 minutes remaining and Cuenca was introduced for Xavi close to the end.
Alexis had to come off anyway, while all three changes arrived after Barca had gone behind and the earlier introduction of Cuenca, in particular, would have livened up a Catalan attack struggling to break down the Blues.
BALLS OVER THE TOP
Probably the best chance of the whole match fell to Alexis after just nine minutes, when Iniesta sent a glorious ball over the Chelsea defence and left the Chilean clean through on goal, only for the South American to beat Petr Cech but not the crossbar when he really should have given Barca the lead.
The Catalans lack height throughout their team but could have made better use of this tactic as the match wore on, with Messi and Alexis ideally suited to these kind of balls, and Iniesta, Xavi and Cesc adept providers. Unable to find their way through at ground level, looking to beat the Blues back line with balls over the top was an obvious option - but one Barca failed to take advantage of after Alexis' early miss.
Gerard Pique was an ideal choice for Barca's battle at Stamford Bridge as the Catalans conceded a notable height advantage to Roberto Di Matteo's men. But the Spain centre-back was left on the bench and Guardiola may have regretted that choice after Javier Mascherano failed to cut out the ball which led to Chelsea's goal.
Mascherano was preferred to Pique again in the Clasico on Saturday - and that didn't work out either. The Catalan defender will play on Tuesday, but he would have been extremely useful in the first match at Stamford Bridge as well, possibly even as a target man in attack as Barca chased the game against a Chelsea team who were coping comfortably at that stage of the game.