With Barcelona suffering a shock home defeat by Malaga on Saturday, Real had a chance to go four points clear and they grabbed it with second-half goals by Karim Benzema and Ronaldo.
Although the Portugal forward struck a curling shot against the post after four minutes, Real struggled to break down a team that worked hard and were guilty of some aggressive challenges.
Benzema was unlucky to have a spectacular overhead kick ruled out due to a questionable offside call but he did knock a loose ball in from close range after 56 minutes.
Ronaldo then sealed the victory with a powerful header into the top corner from an Isco cross after 70 minutes.
It was a welcome goal for Ronaldo who has suffered a dip in form since Christmas following an electrifying start to the season and has now moved joint third in Real’s all-time list.
The Portuguese now has 290 goals and is level with Carlos Santillana, while Raul is out in front on 323.