Kentucky Derby: 80-1 outsider Rich Strike pulls off historic upset

An 80-1 outsider has won the Kentucky Derby, in one of the biggest upsets in the history of America's most celebrated horse race.

Rich Strike - ridden by Sonny Leon - stormed to victory at Churchill Downs in Louisville despite having the longest odds among all 20 horses.

The horse was only brought in on Friday after another had to drop out.

It is the second longest shot to win the Run for the Roses after Donerail won at 91-1 odds in 1913.

Rich Strike pulled ahead down the stretch to beat favourite Epicenter, who was second, and Zandon, who was third.

It was the first Kentucky Derby win for trainer and Kentucky native Eric Reed.

"I fell down in the paddock when he hit the wire," Mr Reed said.

"I passed out. I'm so happy. This is the reason everybody does this. We're not supposed to be here but I knew this horse loved this track and he has been training so good all year."

The trainer had considered walking away from the sport after he lost 23 horses in a barn fire in 2016.

Despite being the outsider, owner Rick Dawson did not seem surprised by the outcome.

"We always felt like if we could just get into the race, we'd have a shot, and we proved it today," Mr Dawson said.

"We've never entered a race we didn't think we could win. Ever."