Karim Benzema put Real Madrid ahead seconds before half-time with a fine finish but it was not until added time at the end of the match that Cristiano Ronaldo at last found the net, his 500th goal of his club career, although there was initial confusion over whether the video referee had decided that the goal should be disallowed for offside.
Madrid were largely comfortable against the winners of the CONCACAF Champions League but they missed a number of opportunities to make the scoreline more emphatic.
Ronaldo had hit the post and missed an open goal either side of the strike from Benzema that made him the first Madrid player to score in two different Club World Cup tournaments.
America battled well but failed to create any meaningful chances of their own against a Madrid defence shorn of captain Sergio Ramos, who was rested with a minor injury worry.
The victory extended Zinedine Zidane’s side’s unbeaten run to 36 games and sets up a final against the champions of Asia Kashima Antlers on Sunday.