Once Didier Drogba had converted Gerrard's disastrous 33rd-minute back-pass the life drained out of Liverpool and Frank Lampard's close-range goal nine minutes after the interval applied the finishing touch.
"I never had the time to think about it," said Ancelotti of Gerrard's back-pass.
"It was an important goal because that goal changed the game.
"We had more confidence after that and Liverpool lost some of the strength they showed in the first 30 minutes."
Drogba told Sky Sports 1: "He made a big mistake. I was lucky to be there and score. It was good because this goal gave us a lot of confidence to play well."