Ronaldo has found the net with remarkable regularity this season, converting 28 times in just 22 appearances.
Saturday's 2-1 win over Malaga was a rare game in which the Portuguese failed to add to his tally, although Ancelotti still thought he was the key man.
He said: "I liked a lot Cristiano because he did an awesome job and I think he was the key of the match.
"He did things we are not used to seeing from him as he didn’t score but made two assists and I think the big part of this victory is his."
The game suddenly became nervy for Madrid who, having been 2-0 up, were reduced to 10 men when Isco was sent off.
Roque Santa Cruz then set up a tense finale by nodding home in injury-time, although Ancelotti's men took the points.
The head coach added: "I am a bit surprised with these players who weren't used to work defensively in the past but here they do, like Isco, [Toni] Kroos, James [Rodriguez] or [Gareth] Bale.
"Those things surprise me. The team is very compact. They work together and as I have said many times, defending is a question of sacrifice."
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