Even with several players missing - not least Cristiano Ronaldo - Madrid had far too much for their hosts.
Adebayor scored the simplest of openers in the 23rd minute before Benzema added a second moments later.
Pablo Pinillos' awful penalty wasted a chance for Racing to get back into the game, and although they briefly threatened after Kennedy Bakircioglu did get a goal, Benzema quickly ended the threat with his second.
Adebayor missed a late penalty, but Madrid had already done enough to move back seven points behind leaders Barcelona.
Racing launched an ambitious penalty claim in only the seventh minute when Xabi Alonso's clearance struck Sergio Ramos at point-blank range, though judging by what would later follow from Pinillos, a penalty would be of little use to them.
It was otherwise one-way traffic in the first half, with Angel Di Maria and Marcelo both spurning chances in the early going.
Marcelo was guilty of the worst miss, latching on to a superb threaded ball from Di Maria and rounding the goalkeeper, only to blaze wide while off-balance with the goal gaping in front of him.
That came only moments after Alonso had struck the crossbar, apparently unintentionally, with a searching free-kick into the box.
Markus Rosenberg gave the home fans a bright spot in the 17th minute, with his twisting run pulling Pepe this way and that, before his off-target shot was nevertheless pushed out for a corner by Casillas, who seemed unaware of his position.
Benzema tested out the framework of the Racing goal again with a powerful shot that came back off the post, just seconds before the breakthrough came.
It was Mesut Ozil who created it, first playing a one-two with Benzema and then another with Adebayor to jink his way through the defence, and then putting it on a plate for the Togolese striker to tap home.
The second goal came four minutes later, Ozil again the provider as his pass with the outside of the boot split the defence and Benzema slotted the ball into the corner of the net.
The Frenchman might have had a second in the 32nd minute when he cut inside, but Marc Torrejon charged down his bending shot.
He made a great turn to shoot five minutes before the break, but Antonio Tono made the save with his foot.
Racing had a chance to get back in the game in the 52nd minute when Alonso's clumsy challenge felled Giovani Dos Santos in the area, but Pinillos' awful penalty was easily saved by Casillas.
But even if they kept their two-goal advantage, Madrid looked subdued and sluggish, allowing Racing to dominate possession.
It cost them in the 70th minute when Mehdi Lacen's pass found the run of Kennedy, who took the ball clear of the Madrid defence before tucking his shot under Casillas and into the corner of the net.
Racing looked inspired and continued to attack, but they failed to test Casillas again before Madrid scored the decisive third on the break.
Di Maria ran from the centre of the field before flicking a pass out to Benzema, who came in from the left to bend a shot past the goalkeeper, making it look easy.
Adebayor missed the chance for his second with another dismal penalty after Torrejon brought down Di Maria in the area, while Ozil looked to have rounded Tono only to take a touch too many, allowing the goalkeeper to recover.