Curlin, with jockey Robby Albarado aboard, ran away from the field with about 330 yards to go. Last year's Horse of the Year continued to increase his advantage down the stretch as he went on to win by 7 3/4 lengths.
The time for the Dubai World Cup was 2:00.15, the third fastest time for the event.
Asiatic Boy, with John Murtagh riding, finished second with Well Armed fading to third and A.P. Arrow closing for fourth after starting from the far outside.
Curlin, winner of last year's Breeders' Cup Classic, earned $3.6 million in winning the richest horse race in the world. He has now won eight of 11 lifetime starts for $8.8 million.
Last year as a 3-year-old, Curlin won the Arkansas Derby, Preakness Stakes and the Jockey Club Gold Cup. He was third in the Kentucky Derby and second in the Belmont Stakes.