"The first match of the season was a good test," Ancelotti said. "We played with commitment and showed good desire and concentration.
"Flamini is a complete player who can be used in the defensive phase as well as the offensive phase.
"For those of us who already know him, he isn't a gamble but a certainty."
Ancelotti was also pleased with the showing of young defender Luca Antonini, back at Milan after a year away with Empoli.
"Antonini has showed that he does better at the back and I think that he can also do well as a winger," Ancelotti stressed.
"He must understand the needs of the team but he provided great dynamism and a lot of will."