Ballon d'Or winner Cristiano Ronaldo thumped in his 31st goal of the season as early as the 10th minute, before Gareth Bale doubled the advantage with a free-kick 15 minutes later.
Karim Benzema put the result beyond doubt in first-half stoppage time - his 100th goal for the club - before further goals in the second period for Angel Di Maria and Alvaro Morata put the gloss on the scoreline.
It was Madrid's seventh straight win in all competitions, and Carlo Ancelotti's side have now racked up five consecutive clean sheets.
The visitors saw Raul Baena dismissed after just 18 minutes, and Edu Albacar put the home side in front from the resulting penalty.
Elsewhere, Sergio Garcia's 88th-minute goal earned Espanyol a 1-0 at home over Celta Vigo while the game between Granada and Osasuna finished goalless.
