Roberto Carlos scored from the penalty spot after 33 minutes and Roberto Soldado and Robinho extended the lead after the break.
But Racing staged a stirring comeback with Sergio Matabuena scoring twice in the last 14 minutes as the visitors wobbled.
Real have 69 points with two games left to play, one ahead of third-placed Valencia, who lost 2-1 away to Real Mallorca on Wednesday.
Valencia's defeat allowed Barcelona to retain their Primera Liga title, as their 1-0 win at Celta Vigo saw them climb to 79 points with a game in hand.
Osasuna are fourth on 65 points after beating Atletico Madrid 1-0.
At the foot of the table, Racing stay 17th, one point above the relegation places.
Real laboured to string together moves early on in Santander and were missing Ronaldo and Julio Baptista up front.
They always looked the side more likely to score, however, and earned the breakthrough after 33
Roberto Carlos placed the spot kick in the corner and was instrumental in helping Real double their lead.
The Brazilian left-ack broke through midfield on a surging run into the area after 60 minutes, only to be denied by Racing keeper Dudu Aouate.
But the ball broke to Raul who shot towards the far post for reserve eam striker Soldado to poke the ball in the net.
Robinho appeared to have put the game beyond Racing in the 70th minute, firing low into the corner from the edge of the area, after good work from Guti coming in off the left flank.
Racing mounted a desperate late assault and pulled a goal back when Matabuena fired home from a crowded penalty area, as Real struggled to clear a corner.
The home side continued to pile forward as Real rocked, and in the final minute a low free kick was allowed to rebound around area before Matabuena bundled the ball across the line.
