The Portugal international gave Madrid a 12th-minute lead at Santiago Bernabeu on Saturday as he collected Karim Benzema's left-wing cross and fired into the far side of the goal.
Benzema and Ronaldo then reversed roles as the Frenchman doubled Madrid's lead, before the former Manchester United man scored a penalty and Sami Khedira netted the fourth.
Antoine Griezmann pulled one back for Sociedad, but Ronaldo rifled in a free kick 14 minutes from time to complete his third hat trick of the season and his 19th in La Liga since moving to Spain in 2009, leaving Ancelotti in awe of his current form.
"Right now Cristiano is out of this world," the 54-year-old said.
"He is playing with incredible consistency and scores a lot of goals. It's difficult to find the words to describe him."
Ancelotti also praised the players who are finding themselves rotated most weeks, as he added: "A team has to play in a way to use all the characteristics of its players.
"Khedira has enough quality to play for Real Madrid. He is consistent and always helps the team.
"Xabi Alonso has a lot of experience and quality to help us play the way we want to play; I've said it many times.
"There are important players on the bench such as [Angel] Di Maria and Isco. We have many options in midfield."