Petr Cech puts Chelsea defence on alert for repeat Champions League show against Barcelona at Nou Camp I think the performance was all about the concentration to stay focused and disciplined all the time to not give them space - even though sometimes for some minutes you don't even see the ball because they are just passing it around and around and around and waiting for their chances. You have to adapt and not get frustrated. It's tough. We've done what we could, we've done really well, but we know we are far away from going through because they will have home advantage for the second leg and everything can happen. At the heart of Chelsea's rigid backline was the resolute figure of Gary Cahill, although the England international believes they will have to score in the return leg to win the tie. "I think we can score in the Nou Camp," Cahill said. I think we will get a chance in 90 minutes. The lads say the pitch is massive. It's going to be tough. Playing them on any pitch will be tough, but playing them on their massive pitch will be extra tough. But if we put in a performance like we did in the first leg then we will not go far wrong. It's going to be tough to keep a clean sheet. We will have to score. We're under no illusions how tough it will be away from home, but we've made a great start. Chelsea will need another imperious target-man performance from Drogba in the Nou Camp if they are going to complete the job. "It was a difficult game for me," said Drogba, who was crucial as an outlet playing on his own up front. Every time I got the ball I looked up and the goal seemed really far away, like on the M25. It's quite difficult to play against them. They are really a good team. Drogba was crushed by Andrés Iniesta's late equaliser when the teams last met in a Champions League semi-final in 2009 and he feared history would repeat itself as Barcelona searched for an equaliser. "We all had that thing in our minds that it was going to happen again to us, but luckily they did not score," he said. I don't think we had anything to prove. What we have done in the past few years is already a big achievement. We just play to qualify. Barcelona, who have to play Real Madrid tomorrow evening, are still confident they will progress to the final, although Iniesta admitted they had been badly wounded. "This is a bad result but we will try to turn it round," he said. There are still 90 minutes left. In the second leg, we expect them to sit deep and wait for us, playing on the break. We will have to be very aggressive when it comes to trying to create chances and to attacking them. We have to be careful though because the result is a difficult one. We have to have the same mentality that we had there: we have to attack them.