City of Troy was never in contention as Sierra Leone won the Breeders’ Cup Classic at the Del Mar track in California.

The Derby winner had been aimed at a glorious farewell in the prestigious US race which carries a purse of $7m (£5.4m), making it the richest horse race in North America.

But he struggled in his first race on dirt as Sierra Leone came from way back to clinch victory at the scenic coastal track in San Diego.

The early leaders set a quick pace and the 6-1 shot rallied past the 5-2 favourite Fierceness in the final stretch.

That gave French jockey Flavien Prat his sixth Breeders’ Cup win overall and trainer Chad Brown his 19th, while Japan’s Forever Young, which closed at 4-1, was third with the Frankie Dettori-ridden Newgate fourth.

Ridden by Ryan Moore, City of Troy ultimately finished eighth in his last race before a breeding career having claimed seven wins from nine races.

His Irish trainer Aidan O’Brien said: “He was left at the start where he lost three lengths and we didn’t have him prepared to break quickly enough. We thought we had, but we hadn’t. He was making up ground at the end, but Ryan had no chance.

“He inspired us as a horse that could do well in the Classic. When you get back that far on a dirt surface, you can’t do anything about it.”

O’Brien is still seeking his first Classic win after 18 attempts with 15 different horses, with his closest effort coming 24 years ago when Giant’s Causeway was edged out by Tiznow.

“We’re learning all the time,” added O’Brien, 55. “Hopefully we’ll try harder next year.”

Sierra Leone had lost narrowly in his last four races including the Kentucky Derby and Belmont Stakes.

“I’m so happy for the horse because he’s come up short a few times,” said trainer Chad Brown.

“He’s been so consistent and he’s such an honest horse, one of the best I’ve ever had.”