Chelsea captain John Terry felt homework was the key to their clean sheet at Barcelona in the first leg of their Champions League semi-final.The hosts largely dominated the game but could not find a way past the Chelsea defence and goalkeeper Petr Cech as Guus Hiddink's side held out for a goalless draw.Terry told ITV1: "They had a lot of possession but we stayed very tight. We watched videos before the game; they like to play little balls through and we knew that and stopped them doing it."It's a fantastic result and we go back to the Bridge ready to go again."It could have been even better for Chelsea had Didier Drogba converted a golden chance in the first half but he was twice denied by Victor Valdes.Terry, though, refused to blame the striker, saying: "I thought Didier was unlucky with both. We didn't create too many chances but we haven't conceded."Barcelona had a strong appeal for a penalty in the second half when Jose Bosingwa appeared to pull back Thierry Henry but Terry felt the referee made the right decision.He continued: "No I don't think (it was a penalty). It's an intimidating place for players and referees to come."We'll have home advantage so hopefully we can make the most of that," he added.