Benzema scored Real’s second goal in the 65th minute in Helsinki, after David Alaba had opened the scoring in the first half.
“I think (he is the best), yes,” Ancelotti said.
“He is our most important player right now, the most efficient player in the world at this moment.
“Karim was the most important in the Champions League, even though he did not score in the final, because of his (all-round) game and his goals got us to the final, against Manchester City and Chelsea, against Paris Saint-Germain.
“He’s very important for us. There is no doubt, at the moment, that he is the best player in the world.”
In the process, he became the club’s outright second-highest goal scorer, having netted for the 324th time for Madrid.
Benzema also became Real’s second highest goal scorer in club history with his strike in the Super Cup.
That goal was his 324th for the club, putting him ahead of Raul and behind only Cristiano Ronaldo (450).