Madrid pulled to within one point of leader Barcelona which later visits a Sevilla side that hasn't lost at home in more than a year.
Ronaldo sent a bouncing free kick over the wall and beyond goalkeeper Xabi Irureta in the 21st minute at Santiago Bernabeu Stadium.Little-used striker Javier Hernandez doubled the lead in the 31st, and youngster Jese Rodriguez capped the one-sided match in the 83rd.
Madrid was able to give some of its regular bench players a rare start while several first-choice starters rested ahead of its Champions League quarterfinal at Atletico Madrid on Tuesday.
Gareth Bale missed the match with a muscle strain. Coach Carlo Ancelotti started Hernandez instead of Karim Benzema, while Keylor Navas had a quiet day in goal replacing Iker Casillas. And the team didn't miss midfielders James Rodriguez and Toni Kroos, who served one-match suspensions.
Madrid's defense even got a boost when Pepe returned from injury as a second-half substitute.
Ronaldo received some help from Irureta to score his goal. The Eibar goalkeeper misjudged Ronaldo's free kick and moved out of position, leaving him unable to react in time and stop the ball from bouncing past.
Madrid dominated the rest of the way as Hernandez and Rodriguez polished off the victory that kept Eibar in 14th place.
Also later, third-place Atletico visits Malaga, Celta Vigo hosts Rayo Vallecano and Granada is at Almeria.
Related story
There is more than meets the eye for Barcelona
