I'll Have Another won the Kentucky Derby at Churchill Downs on Saturday before a record crowd of almost 165,000.
The three-year-old chestnut colt won the $US2.2 million race by 1.5 lengths.
Bodemeister, the favourite, was second after trying to lead all the way. Dullahan came third.
"He is an amazing horse," said jockey Mario Gutierrez, who moved to the United States less than a year ago after riding for six years in Canada. He was riding in the Derby for the first time.
"I told everybody before the first time I rode him, I knew he was the one."
I'll Have Another was bought last year by Canadian businessman J. Paul Reddam for $US35,000 and emerged as a contender after winning the Santa Anita Derby in California last month.
He started at odds of 15-1, paying $US32.60 for a $US2 win bet.
The race was preceded by the singing of My Old Kentucky Home and the winner was draped in a garland of red roses.
The Kentucky Derby is the first leg of the triple crown in the United States.
The Preakness Stakes are next and then the Belmont Stakes. It is 34 years since the same horse won all three events: Affirmed in 1978, Seattle Slew in 1977 and Secretariat in 1973.