Cahill struck in the 4-2 extra-time win.
"I know things are new and we are trying to learn different things but we started the game so sloppily," Cahill told chelseafc.com.
"From about midway in the first half and especially in the second half we showed what we want to do and the way we want to play.
"As the game went on we got stronger and stronger and I felt like we were going to get back in it, especially when we got the first goal. If you go in 2-0 up you're comfortable but it gave us a lift. Second half was a good performance.
"We created chances and Cesc scored two to put the game to bed."