The contest, a rerun of one of last season's quarter-finals, might have evolved differently had the normally clinical Burak Y?lmaz not directed a free header wide within two minutes of the restart. Karim Benzema punished the hosts soon after, adding to Isco's composed 33rd-minute opener.
Two goals in quick succession from Ronaldo and a close-range Benzema finish increased the Merengues' lead, before Umut Bulut struck a consolation for Cimbom. Ronaldo's third meant the Spanish side posted their biggest away triumph in the UEFA Champions League and inflicted Galatasaray's heaviest home defeat in Europe.
The end result seemed implausible as Galatasaray made a strong start, pushing Madrid back. Felipe Melo tested Iker Casillas with a 20-metre shot, but the Spain No1's evening – his first club appearance of the season – was soon curtailed by a what appeared to be a rib injury sustained in an earlier collision with Sergio Ramos.
His replacement, Diego López, was quickly pressed into service, showing why he has kept Casillas out of the side for much of 2013. Having denied Melo from a free-kick, López pulled off a diving save on the half-hour mark, throwing himself to his left to palm away a header from the same player following Wesley Sneijder's corner.
Within three minutes the visitors were in front, Isco expertly controlling Ángel Di María's diagonal pass and rolling a shot in off Fernando Muslera's right-hand upright. After Burak failed to turn in substitute Nordin Amrabat's floated cross, Carlo Ancelotti's men ran away with the game.
First, Benzema raced on to Di María's touch and slipped the ball beyond Muslera for Madrid's second, a hammer blow to Galatasaray which was swiftly followed by two straightforward Ronaldo finishes.
The Portugal captain turned provider for Benzema with nine minutes left and, though Umut pulled one back for Fatih Terim's team from Amrabat's centre, there was still time for Ronaldo to glide past three challenges and complete his second treble in Europe's premier club competition./UEFA/