American Pharoah has become the first horse to win the US Triple Crown since 1978.
The three-year-old added Saturday's Belmont Stakes in New York to earlier wins in the Kentucky Derby and Preakness Stakes, emulating a feat last achieved by Affirmed 37 years ago.
Ridden by Victor Espinoza, American Pharoah dominated to win comfortably from Frosted and Materiality.
Espinoza, 43, becomes the oldest jockey to have won the Triple Crown.
Trainer Bob Baffert said: "I knew he was training well, but you have to have the horse. It's not down to me - it's the horse."
Twelve horses have now secured this prestigious treble, since it was first achieved in 1919 by Sir Barton.