Triple Crown winner American Pharoah came up short in the $US1.6 million ($A2.23 million) Travers Stakes on Saturday, losing to Keen Ice by three-quarters of a length before a sold-out and stunned crowd at Saratoga Race Course.

American Pharoah came into the race as the overwhelming favourite, but the first Triple Crown winner in 37 years lost the lead entering the far turn.

He pulled closer to Keen Ice entering the stretch but was unable to muster the extra energy he usually finds to overtake the powerful final run of the 16-1 long shot.

The upset solidified Saratoga's reputation as the "Graveyard of Favourites." Only one of 12 Triple Crown winners has been able to go on and win the Travers - Whirlaway in 1941.

Keen Ice, a three-time loser to American Pharoah entering the Travers, was ridden by Javier Castellano, who won a record-setting fifth "Mid-Summer Derby."

"I feel bad for the horse getting beat like that," a disappointed trainer Bob Baffert said. "You can tell he wasn't on his 'A' game. Pharoah dug in, but Keen Ice ran a great race."

Trained by Dale Romans, Keen Ice ran 1-1/4 miles (2000m) in 2:01.57.

American Pharoah, losing for the first time after eight straight magnificent wins, was the 1-5 favourite in the 10-horse field.

"He's OK," American Pharoah jockey Victor Espinoza said. "Maybe just a little too much for him with the three weeks flying back and forth. He was running pretty comfortable there, but not like he used to before."

Frosted was third, with Upstart fourth and Texas Red fifth. Frammento and Smart Transition dead-heated for sixth, followed by Tale of Verve, Mid Ocean and King of New York.