Didier Drogba scored deep in to first-half injury-time to give the Blues the advantage.
"It was a fantastic result but it's only half-time," Cahill said.
"I thought as a team tonight we were well organised. Everyone was on the same page.
"The gaffer gave us a game plan before the game and we stuck to it. It worked really well, but it's half-time and it's going to be really hard over there but it's a good start for us."