Indeed they were denied by absolute perfect defending by Chelsea. They didn't see many opening but they did create an almost perfect four opening, only to be denied by Cech and a lack of cool heads by their own players. But our midfield, eventhough did not create much opening was perfect in ball possession. People, especially English media will say - "What's there with Ball Possession, if you can't get the goals!". But there were positives to look at Stamford Bridge from the performance of our midfield. Chelsea midfield had Essien, Malouda, Lampard, Obei Mikel and Ballack in their ranks and we had the likes of Iniesta, Xavi and Toure. Out of the three Toure is the only one who has a physical built which could challenge any of those midfielders, but to their credit Barca midfield did creat some trouble for Chelsea, especially Iniesta. Mikel might have kept Xavi quiet from creating chances but not from retaining possession.
The two reason why Barca failed to create much of chances were the decision by Chelsea to lay deep in their half and most importantly a lack of pace. FC Barcelona played the game at a lower pace than they normally used to. This has to be predominantly attributed to the poor game Messi and Eto had. But with the tie remaining at 0-0, we can expect Chelsea to open up a bit towards the end of the second tie. Chelsea's startegy would be the same as the first leg and to neautralise that we have to take extreme caution not to give Cheap balls away to Chelsea at decent positions. If we manage to do that Chelsea eventually had to open up, giving us space to exploit. For what all Chelsea players and English media might claim, in football you have to score goals to win. And that makes the tie evenly poised.
NB: You will here claims from English media and Chelsea players about how they are going to attack Barca at Stamford Bridge. Don't give a damn to those, as we all know they will start playing the same way as in the first leg.