Joseph O'Brien has become the youngest jockey, at the age of 18, to win a Breeders' Cup race by triumphing on St Nicholas Abbey, a horse trained by his father Aidan.
St Nicholas Abbey beat Britain's Sea Moon to win the $3m (£2m) Breeders' Cup Turf race at Churchill Downs, Kentucky.
Settled in mid-division, the Montjeu colt picked up superbly when angled out for a run.
Sea Moon had no answer in second, with Brilliant Speed third.
St Nicholas Abbey had taken the lead in the stretch and hit the wire two and a quarter lengths ahead of Sea Moon.
Joseph O'Brien said: "It's a dream come true. I've been coming to the Breeders' Cup since I was very small, but to ride here and ride a winner - it's out of this world."
Aidan O'Brien claimed his second Breeders' Cup race of the day after winning the Juvenile Turf with Wrote.
Speaking about his son's win, he said: "This is very special. Unbelievable. It was a wonderful race. He is an amazing rider."
The Breeders' Cup is an annual series of thoroughbred horse races, which is being held over two days this year.
Since the inaugural running at Hollywood Park 27 years ago, it has become the season-ending championship of thoroughbred racing.
