Harzand, ridden by Irish jockey Pat Smullen, held off favourite US Army Ranger, to win the Epsom Derby on Saturday.

US Army Ranger appeared to be poised for victory with a well-timed burst but never got level with Dermot Weld-trained Harzand who stretched away to triumph in the world-famous flat race.

"I spotted the white face of US Army Ranger, but this horse responded to me," said reigning Irish champion jockey Smullen, riding in the colours of owner the Aga Khan.

"The race went well, it was tough late on but this horse is great."

Idaho was third.

Harzand suffered an injury scare on the morning of the race when blood was found on his foot, but the 10-1 shot, a renowned stayer, was declared fit to start the high-speed 12-furlong classic.

"We had a huge worry when he spread a plate travelling over," Weld, who has also trained winners of the Irish Derby, Belmont Stakes and Melbourne Cup, said.

"He was a very doubtful runner up until about an hour ago but with the help of all of my team, we made it."

The first prize was STG876,000 ($A1.75 million).

There was disappointment for Frankie Dettori who had been hoping to win his second successive Derby on board second favourite Wings of Desire.