Benzema brace sinks Santander
Ronaldo, who has netted 27 goals this season, missed his first league game of the campaign with a muscle strain, but Benzema and Emmanuel Adebayor led Jose Mourinho's side on to 67 points with 11 games left.
Barca beat Real Zaragoza 1-0 at home on Saturday. Real made a flying start at the Sardinero, hitting the crossbar twice before Adebayor scored in the 23rd minute following the type of move more usually associated with their arch-rivals Barca.
The outstanding Mesut Ozil was at the centre of a series of one-touch passes which sliced Racing open and he finished by squaring for Adebayor to sidefoot into the empty net.
Three minutes later, the Germany midfielder set up Benzema to score the second.
Racing, who had not lost under new coach Marcelino, spurned a chance to hit back when Pablo Pinillos's weak penalty was saved after the break, but Kennedy Bakircioglu threatened a comeback when he scored from a fine move in the 70th.
Benzema curled in his second soon after following a counter-attack and Adebayor also missed a late penalty.
"We played very well, very compact and controlled the game," Mourinho told reporters.
"We should have had the game won in the first half. Racing scored a goal but again we had a good reaction from the team."
Earlier, a Sevilla own-goal and a late penalty from Andoni Iraola gave Athletic Bilbao a 2-0 home win which lifted them to fifth.
The Basque club moved on to 41 points from 27 games, nine short of Villarreal and the last Champions League qualification slot. The fourth-placed side lost 3-1 at Atletico Madrid on Saturday.
Sevilla's Argentine defender Federico Fazio knocked a cross into his own net with his knee after 66 minutes, in a bruising encounter at San Mames.
Julien Escude brought down Oscar de Marcos for a penalty which Iraola, wearing a head bandage after a collision with Sevilla's Alvaro Negredo, converted in the 88th.
Negredo, strike partner Luis Fabiano and Bilbao's Gaizka Toquero all had to leave the pitch with injuries.
Levante striker Felipe Caicedo, on loan from Manchester City, bagged his 11th goal of the campaign, a first-half header giving his side a 1-0 home victory over misfiring Espanyol.
The Barcelona-based side have lost six of their last seven games and dropped further off the pace in the race for the Champions League, going down to sixth with 40 points.
Malaga slipped back to the foot of the standings on 23 points with a 1-0 home defeat by Osasuna, when Sergio Fernandez scored at the end to give the Navarans their first away win of the season.
Almeria climbed two points above Malaga into 19th with a 2-1 comeback win at Hercules, who now occupy the last relegation place in 18th on 26 points. Sporting Gijon moved out of the bottom three with a 2-0 home win over Getafe.