Ronaldo struck four times in a dominant display at The Santiago Bernabeu on Tuesday as Real claimed a come-from-behind 5-1 win.
Questions were raised in the lead up over whether the Portugal international needed an extended rest.
But Ancelotti said Ronaldo's performance was proof he was fit, motivated and in fine form.
"Ronaldo rested when he did not play with Portugal [over the international break] and he needed a period of work," he said.
"He trained with a lot of sobriety and being very professional and in this moment he is very good physically and he is very motivated and he scores a lot."
Ancelotti felt his team were in control after Gareth Bale equalised in the 20th minute, cancelling out Edu Albacar's early penalty.
Keylor Navas started in goal for Real as Iker Casillas was benched, and Ancelotti was content with the Costa Rican goalkeeper's performance.
"He played with security," Ancelotti said.
"I think that in defence the duties were shared well and Keylor did not have too much work but he was very calm."
Ancelotti said he would continue rotating his squad, with Karim Benzema and Luka Modric to return against Villarreal on Saturday.
"I think in this moment the rotation is very important because we have all the players motivated," the Italian said.
"There are a lot of games to be played and we play on Saturday so I think it is normal at this moment to rotate players and avoid problems.
"Today Benzema and also Modric are resting and they will play on Saturday."