Prince Bishop left racing fans scratching their heads when he cut down the rags-to-riches American horse California Chrome to win the $10 million Dubai World Cup on Saturday.

It was a stunning outcome at the world's richest race, and one virtually unforseen by the 60,000 spectators at Meydan racecourse.

The stage looked set for California Chrome to join a hallowed cast of previous winners when jockey Victor Espinosa moved his mount into a challenging position rounding the turn for home.

But jockey William Buick aboard Prince Bishop had other ideas.

Having countered Espinosa's move, Buick drove his mount past the sentimental favourite en route to a decisive victory by 2 3/4 lengths.

The second American challenger, Lea, finished third, one place ahead of local hope Candy Boy.

"I don't go numb very often but I can't explain what I'm feeling right now," Buick said. "This is just nuts."

It was the fourth time Prince Bishop, who is trained in Dubai by Saeed Bin Suroor, had contested the World Cup.

He finished ninth last year, seventh in 2012 and tenth the previous year.

His victory earned his owner, Sheikh Hamdan bin Mohd al Maktoum of the Dubai ruling family, the winner's purse of $US6 million ($A7.67m).

Bin Suroor was posting his seventh triumph in the race. He won it 12 months ago with African Story but that horse could finish only sixth this time under Bin Suroor's senior jockey, James Doyle.

Japan's pair of champions, Hokko Tarumae and Epiphaneia, could finish only fifth and last respectively in the nine-runner field.

Art Sherman, who trains California Chrome, was magnanimous in defeat.

"Second money is not bad at all," he said.

"He ran his eyeballs out. He was right there in contention all the way.

"The horse you think is going to win doesn't always. That's what happens in this game."

Espinosa was equally philosophical.

"He (California Chrome) kind of lost his stride a little bit on the home turn because the horse on my inside (Hokko Tarumae) pushed me out. But overall, he ran awesome."

Prince Bishop's victory was unexpected because he had run on Maydan's dirt surface twice before and resented the sand kickback that sprays horses in the face. However, he had finished strongly once he found clear air.

Buick's role in his World Cup victory was pivotal. He had ridden Prince Bishop on his last two starts and recognised the importance of having a clear track ahead of him.

"Saeed told me to avoid getting kickback if at all possible," the jockey related.

"I knew that that was the best way to maximise my horse's chance. He has a very unorthodox way of racing but he ran on well to the end."

Buick forged his path to victory when he secured a place on the outside of the field from his inside gate draw in stall one.

He was always within striking distance of a gallop dictated by Hokko Tarumae and pounced on California Chrome early in the home straight.

An eight-year-old horse, Prince Bishop is the oldest winner of the Dubai World Cup.

This was his eleventh victory from 28 starts. It was by some way the most significant.