With two goals in the semi-final and final, Cristiano is now the all-time leading marksman in the competition with seven goals.
In the final, Ronaldo broke the deadlock eight minutes after the interval when he clipped the ball over the wall and into the bottom corner.
The hard-earned victory over a stubborn Grêmio side at the Zayed Sports City Stadium was Real’s third Club World Cup since 2014, equalling the record of their La Liga rivals Barcelona.
The Spanish champions started brightly when Karim Benzema’s effort was deflected behind. Ronaldo then curled a shot wide before Isco fired over.
As the half-hour mark approached, the Brazilian side had a chance to threaten when Casemiro conceded a free-kick thirty metres out with Edílson’s long-range effort just too high.
As half-time approached Cristiano Ronaldo signalled his intent when he fired in a free-kick, from distance, which was narrowly too high. The Champions League holders continued to press early in the second-half, Ronaldo sending another long-range shot wide before the deadlock was finally broken.
Ronaldo was tripped just outside the Grêmio penalty area by Jailson and the Portugal captain got up, brushed himself down and then proceeded to arrow the ball over the wall and into the bottom left corner past the despairing keeper. Grêmio, who beat the Mexican side Pachuca to secure a place in the final, were then forced to go on the attack but lacked any real threat. It looked as if Real had scored again just before the hour, but Ronaldo’s effort was ruled out by an offside flag. The Grêmio goalkeeper, Marcelo Grohe, then pushed an effort from Luka Modric on to the post as Real continued to press.
With ten minutes left Gareth Bale replaced Benzema and the Wales forward soon forced Grohe into another good save, this time tipping his curling shot over.
Real Madrid became the first team to retain the trophy and skipper Sergio Ramos, who has won eighteen titles with the club, has lifted a major trophy on five separate occasions this year.