Both their goals came from corners, with Branislav Ivanovic and Nicolas Anelka punishing slack defending.
Ancelotti said: "If I have to judge the performance today, I can say it was good.
"We could score before the first goal of Ivanovic, we could score in the first half. But our play was good, more intensity, more quality."
He added: "It was important also for us to score on the set pieces.
"We had a lot of opportunities today. Ivanovic is very good with his head, he scored in an important moment.
"After the first goal, the team played a good game.
"Obviously, we want to score with good play, with good football. But also we have to use the set-pieces because I think we have dangerous players in the set-pieces."
"We needed to have more size," Ancelotti said.
"I knew that Blackburn could use long balls and set-pieces.
"So I wanted to have power in the box. For this reason, Essien and Drogba started the game."