Karim Benzema fired into the roof of the net from the edge of area in the 36th after Mesut Oezil skillfully laid the ball into his path, before Alvaro Arbeloa doubled the Spanish side's advantage with a fierce shot in the 44th.
Arbeloa then set up Ronaldo to make it 2-0 with a close-range shot and the Portuguese winger completed the scoring from the spot in the 80th.
Madrid's night was marred when both Xabi Alonso and Sergio Ramos were sent off late in the game after picking up second bookings.
Madrid has 13 points, five more than AC Milan. Ajax remains third with four.
Benzema, who was deputizing for the injured Gonzalo Higuain in the Madrid attack, almost gave his side the lead in the 18th when he charged past Toby Alderweireld and fired a shot from a tight angle but Maarteen Stekelenburg made a save, palming the ball away.
Two minutes later, Scotland referee Craig Thomson left Ronaldo frustrated when he waved away the Portugal winger's penalty appeal after he appeared to have been fouled in the area by Ajax rightback Gregory van der Wiel.
Madrid had to be patient as Ajax enjoyed spells of possession in the first half even though the Amsterdam giant rarely tested Iker Casillas.
The Spain goalkeeper was only called into action to deal with Jan Vertonghen's thumping free kick in the second half.
But Stekelenburg was forced to make a series of saves to stop a Madrid onslaught.
The build-up to the Madrid goal began with Eyong Enoh's foul on Pedro Leon. Alonso dispatched a long ball deep into the Ajax area, allowing Oezil to invitingly set up Benzema with a first-time pass.
Madrid Hammers Ajax
Comments