Champions League: Chelsea Tries to Buck the System in Barcelona Barcelona's players claimed that "a tear had rolled down the face of the game" after they were felled by José Mourinho's defensive Inter Milan two years ago. That night in the Camp Nou, the Italians commanded only 14 percent of the overall possession. They failed to manage a single shot on goal, and had just one over all, compared with Barça's 20. Mourinho's team even had to play more than an hour of the semifinal second leg with 10 men. But Barcelona was eliminated and Mourinho went on to lift his second European Cup. To hear the purists tell it, soccer had lost, not just Barcelona. Tuesday Chelsea at Barcelona, 2:45 p.m. (Fox Soccer) Sam Borden of The Times is in Barcelona. Read his preview here. Wednesday Bayern Munich at Real Madrid, 2:45 p.m. NOTE TO READERS: The Goal blog will provide live updates during both of this week's games. One can only assume Roberto Di Matteo was taking notes that night, since he guided Chelsea to a 1-0 victory in eerily similar fashion last week in the first leg of this year's semifinals. Just as Inter had before them, Chelsea proved that possession is just a number. That territorial dominance does not guarantee victory. And that Lionel Messi can be stopped. The plan Di Matteo devised saw Chelsea afford Barcelona more possession than any team to have faced the Catalans in the Champions League this season (79 percent). Chelsea also conceded more territorial freedom than it had surrendered all season. Crucially, that was all it surrendered, as Di Matteo became only the second manager in more than two years to mastermind a shutout against Barcelona in Europe. But now Di Matteo must repeat the trick if his team is to progress to the final in Munich next month. He must find a way to neutralize an attack that has scored 113 times in 27 home games this season. He must take hope and inspiration from the precedent set by Mourinho and Inter two years ago. After Mourinho orchestrated another impressive performance at the Camp Nou in Saturday's Clásico, the fear factor that accompanies the task facing Chelsea has been dispelled momentarily. Still, the consensus remains that Chelsea stands little chance of duplicating last week's victory. So what can Di Matteo and his players do to once again counter the threats presented by a team many consider to be the greatest to play the game? It is opportunistic to attack Barça on the back of two successive defeats, but given how their season could disintegrate in the space of a week with another defeat Tuesday, the fractures in Manager Pep Guardiola's system have never been more conspicuous. When faced with the task of beating Barcelona, most opt for the Mourinho-Inter model, particularly at the Camp Nou. That involves planting one's backline so close to the goal that there is no empty space for Barcelona to exploit with its famed passing game and its veiled runs behind the defense. The strategy involves affording Xavi and Messi the freedom to do what they like until they reach the edge of the penalty area, where strict zonal marking takes charge. It also involves a generous dose of fortune. It may not be the most dignified strategy, but when conducted to perfection, it can be an effective one. Transition Game The assumption about playing at the Camp Nou is that the vast playing surface presents the home side with an almost unassailable advantage. Indeed, the playing surface is a staggering 250 square yards bigger than the one the sides competed on last week at Stamford Bridge. Logic dictates that more space for Barcelona is more space for Messi, for Xavi, for Andres Iniesta. And that means more danger for opponents. But what few have identified are the defensive vulnerabilities inherent in Barcelona's system. It has become something of a cliché to focus criticism on the Catalans" backline, and on the midfielder-turned-center-back Javier Mascherano in particular. But the flaws lie in the system, not the personnel. In Saturday's Clásico, Dani Alves was often Barça's furthest forward player, providing width on the right side. Because of this, Barcelona's formation is best described as a 3-4-3. When set in either offense or defense, the system can be almost impenetrable. But in the transition between the two lies opportunity. To counter the three-man defense when attacking, Guardiola employs Sergio Busquets as something of a false center back. Barcelona is quick to snap back into a four-man defense when it loses possession, with Busquets slotting into the back to compensate until Alves retreats. But if a team can attack faster than Barcelona can react, Carles Puyol and Mascherano can become victims of the system. Fans have seen this twice in the past week, with both Chelsea and Real Madrid attacking on the flanks at pace on the counter. The misconception is that these flaws don't exist when playing in the comfort of the Camp Nou's enormous field. In fact, however, the stadium is far from a bastion of indestructibility. European visitors to the Camp Nou will play almost as many attacking third passes as they would at home on average (393 compared with 415), with a slightly higher completion rate (55 percent compared with 53 percent). Even soccer's purest statistic - goals - shows that teams are more likely to score at the Camp Nou than they are elsewhere: Guardiola's teams concede an average of 0.8 goals per game at home in Europe, compared with 0.66 on their travels. These margins are certainly nothing to suggest a Chelsea win in the second leg is anything close to a certainty. While the Blues may statistically stand just as much chance of scoring at Barça as they would in London, they are still extremely likely to be outscored by a lineup that has produced 33 goals in 11 Champions League matches this season. Pressure for Pressure So as understandable as Di Matteo's inevitable defensive approach will be, Chelsea must try to hurt Barcelona going forward. Didier Drogba will be a key figure once again (as long as he can play), with Di Matteo almost certain to opt for him over the naturally deeper-lying Fernando Torres. Drogba's influence going forward, providing the pivot on which to build an attack, will be crucial. Despite a common attitude that Chelsea got lucky last week, Di Matteo need not abandon the plan that worked at Stamford Bridge. But he may need to tweak it. Although Chelsea scored after Ramires exploited the space left by Alves on the right, Di Matteo may need to encourage more frequent capitalization of Barcelona's vulnerable channels. That might mean sacrificing Juan Mata for the more direct Florent Malouda or Salomon Kalou. But the biggest tactical challenge Chelsea will face will be whether to increase its focus on disrupting the Barcelona midfield. If the Blues get this right, it may provide a platform for them to exploit the weaknesses of Guardiola's system in transition. Of course, if he gets it wrong he risks making the same mistakes that Milan did in the previous round, when Barcelona simply passed around them. Chelsea may also have to rely on Guardiola making mistakes in his team selection. The inclusion of Cristian Tello and Thiago Alcantara against Real Madrid on Saturday was met with surprise, and the performances of each didn't do much to vindicate their selection. The exclusion of Gerard Piqué last week also left Guardiola open to criticism, although according to news media reports he will start on Tuesday. Of course, just as the first leg proved, one major factor that will determine whether Chelsea can become the second team to knock out Barcelona at the semifinal stage in the Camp Nou in three years is luck. If all those components come together, if Di Matteo can devise a strategy to suppress one of the most daunting attacking propositions ever seen, if Guardiola can't find a way to redeem himself, then the only tears in Barcelona will be running down Spanish faces. Follow Graham Ruthven on Twitter.