Returning from a two-game suspension, Ronaldo was the chief protagonist throughout for the visitors but in the first half on Saturday Real did not have it all their own way.
Chances for both sides saw Jeronimo Momes and Ronaldo hit the woodwork at either end but after the break Real began to dominate.
Defender Alvaro Arbeloa made the breakthrough after 64 minutes before Ronaldo wrapped the game up with two goals in two minutes.
Kaka was the provider on both occasions for the Portuguese, who scored first with his head and then via a simple side-foot finish.
"Scoring is tough, no matter who the opponent is. We were up against a good Xerez team in the first half," said Real coach Manuel Pellegrini.
Earlier, a cool Juan Mata finish rescued a point for a battling Valencia side, who drew 1-1 against Sporting Gijon.Despite going into the game on the back of four straight defeats, it was Sporting who began the livelier and they went ahead through a fine curling strike from Diego Castro.
Valencia were struggling in defence without David Navarro and Alexis Ruanoes but going forward they began to find their feet, with David Villa -- returning to the club where he began his career -- denied by an inspired Juan Pablo in the Sporting goal.
It appeared as though it was not going to be Valencia's day after they hit the post twice and Mata missed a one-on-one chance with the goalkeeper, as Sporting were forced further and further back.
However, with 14 minutes to go, Ever Banega supplied Mata with an excellent through ball and this time he made no mistake, finishing clinically. In yesterday's late match, Villarreal overcame Athletic Bilbao 2-1 in a hot-tempered game that culminated in three red cards.
Villarreal left-back Joan Capdevila gave his side the lead after ghosting into the box in the fifth minute but the visitors drew level 20 minutes later when Igor Gabilondo cracked an unstoppable 30-yard shot into the top corner.
Brazil international striker Nilmar re-established Villarreal's lead just before half-time and Bilbao spurned a golden opportunity to equalise when Andoni Iraola's penalty was saved by Diego Lopez at the death.
Frustrations boiled over in the game's closing stages, with red cards shown to Villarreal defender Diego Godin and visiting pair Pablo Orbaiz and Javi Martinez. Villarreal climb one place to ninth, four points behind seventh-placed Bilb.