The Spanish champions had been frustrated by Ajax goalkeeper Kenneth Vermeer for most of the first half but finally made the breakthrough just before half-time when Ronaldo tapped in from Karim Benzema's cross.
Benzema then made it two after the interval with a stunning bicycle kick from Kaka's cross but Niklas Moisander briefly gave the Dutch champions hope when he headed in to reduce the arrears eight minutes later.
However, that hope was extinguished with 11 minutes remaining when Ronaldo smashed home the visitors' third from outside the area, before completing the rout with a lovely chip over Vermeer soon after.
Real had needed a very late turnaround to take the three points against Manchester City on matchday one but they were in complete control from the start in Amsterdam tonight and were only denied a bigger win by a string of fine saves from Vermeer.
Unsurprisingly Ronaldo was the first to threaten as he was picked out on the left side of the area - but Vermeer was off his line very quickly to block the Portuguese captain's fierce effort.
Moments later Vermeer was forced into an even better double save as Kaka weaved himself some room inside the box and after his low shot was parried the Dutch keeper was back on his feet quickly to turn away Benzema's attempt on the rebound.
Ronaldo headed another pinpoint Kaka cross straight at Vermeer from five yards out, before Marcelo became the latest Real player to be denied as Vermeer steered away his low shot from the angle of the box.
However the opener arrived four minutes before half-time as Benzema got to the byline and his driven cross was deflected perfectly into the path of Ronaldo to flick the ball home from three yards.
And the nine times European champions started the second period in even greater style as a slick counter-attack saw Marcelo feed Kaka and his cross was volleyed in on the swivel by Benzema.
Ajax scored with virtually their first sight of goal as Iker Casillas got caught underneath Christian Eriksen's corner and Moisander was free at the back post to head home.
Benzema should have restored the two-goal cushion but he wastefully headed over from Kaka's cross five minutes later, then Vermeer produced another stellar save to turn away Angel Di Maria's low drive.
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However, the hosts had a glorious opportunity to equalise after Ryan Babel's cross just eluded Siem de Jong at the near post. Danny Hoesen should have scored - but blazed over at the back post with his first touch.
Frank de Boer's men were left to rue that miss as 10 minutes later Ronaldo sealed the three points, exchanging passes with Benzema on the left before curling a shot from outside the area into the bottom corner.
A minute later he secured his second hat-trick in two games as he raced onto Sami Khedira's through-ball and lifted the ball over the advancing Vermeer into the net.