The fairytale story of California Chrome has continued on the biggest stage with the colt claiming a dominant win in the Kentucky Derby.

Taking charge at the top of the straight, California Chrome (5-2 fav) sprinted clear under Victor Espinoza to give the jockey a second Derby win to go with his 2002 victory on War Emblem.

Art Sherman became the oldest trainer to win the Derby, 57 years after he travelled from California as an exercise rider for Derby winner Swaps.

He watched that race from the barn area. This time he smelled red roses in the winner's circle on Saturday (Sunday AEST).

"It's been a long haul," Sherman said. "I'm just the same old Art Sherman, except I won the Kentucky Derby."

In a sport dominated by wealthy owners and regally bred horses from Kentucky's bluegrass country, this was a victory for the little guys.

Owners Perry Martin and Steve Coburn bred an $8000 mare to a $2500 stallion to produce the winner of the famous race with their one-horse stable.

"This is just a dream come true and a great birthday present," Coburn said as he celebrated his 61st birthday.

He said California Chrome, who extended his winning streak to five, would now head to the Preakness Stakes and the Belmont Stakes in an attempt to become the first horse since Affirmed in 1978 to win the Triple Crown.

Sherman, who became a jockey after his first Derby experience, paid credit to Espinoza.

"I thought he rode him perfect," he said.

"I was riding the last 70 yards with Victor, so I think he was riding two. He had a lot of weight on him, I can tell you that."

Espinoza said he could not explain his bond with California Chrome.

"I don't know why but we get along together very well," he said.

"I let him do his thing. I let him enjoy the race."

The race was watched by a crowd of 164,906, the second-largest in the Derby's 140-year history.