Ronaldo's treble saw Juve defeat Atletico Madrid and reach the Champions League quarterfinals 3-2 on aggregate.
Ancelotti, who won the competition with Ronaldo at Real Madrid, said: "Everybody expects him to lose his ability over the years, but he never drops off.
"Ronaldo never fails, especially in these games, he's the one who makes the difference.
"There are big players who cannot excel in important matches. This is where a great player differs from a great champion, as he is.
"It was an extraordinary feat by an extraordinary player."