Sierra Leone has won the $7 million ($A11 million) Breeders' Cup Classic by 1 1/2 lengths at Del Mar, ending a frustrating run of recent losses, including the Kentucky Derby.

Ridden by Flavien Prat, Sierra Leone was sent off as the 6-1 fourth choice in his first race after a two-month layoff.

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

"I thought he had some excuses, but he's been so consistent and he's such an honest horse, one of the best that I've ever had."

Sierra Leone lost by a nose to Mystik Dan in the Kentucky Derby and then finished third in the Belmont Stakes at Saratoga.

"He took a tough beat in the Derby, but we did it with class and respect, and we just went back to the drawing board and worked on getting him straight," Brown said. "He's a great horse, he took to this track and it was his day today."

Brown has 19 Cup wins, leaving him one short of career leading trainers Aidan O'Brien, who won two races Friday, and D. Wayne Lukas.

It was Brown's first win in the Classic on his fourth try. His mentor, the late Hall of Fame trainer Bobby Frankel, won the Classic in 2004 with Ghostzapper.

"At moments like this, I always think about him," Brown said.

Fierceness, the 5-2 favourite, was second and Forever Young of Japan was another 2 3/4 lengths back in third.

Newgate, trained by Bob Baffert, was fourth in the full field of 14.

Ireland-based City of Troy, the 4-1 third choice with six wins in seven career starts on grass, finished eighth in his first start on dirt for O'Brien.

Prat made back-to-back trips to the winner's circle, taking the $US2 million ($A3 million) Filly & Mare Turf aboard Moira for his 50th graded stakes win of the year.

In the $2 million ($A3 million) Distaff, Thorpedo Anna won by 2 1/2 lengths, helping trainer Ken McPeek snap an 0-for-37 skid in the Breeders' Cup.

"The expectation with her is so high," McPeek said. "I love the fact that Brian took the initiative and just got it done. For me, it was workmanlike and that's what you need."

Hernandez and McPeek teamed to win the Kentucky Derby by a nose in May.

In the $5 million ($A 7.6 million) Turf, 9-5 favorite Rebel's Romance held off late-closing 22-1 shot Rousham Park to win by a neck, the ninth European horse to do so in the last 10 runnings.

Rebel's Romance ran 1 1/2 miles in 2:26.07 under jockey William Buick and paid $5.80 to win. The 6-year-old gelding has been a globetrotter, winning in Qatar, Dubai, Hong Kong, Britain, Germany and the U.S. for trainer Charlie Appleby.

Another horse, 3-year-old France-bred Jayarebe, collapsed on the track after finishing seventh in the Turf and died.

"It was suspected to be a cardiac event," said Dr. Al Ruggles, the on-call veterinarian.

It was an 11th Breeders' Cup win for Appleby who once again showed his prowess at this meeting, although there was to be no dream reunion for John Gosden and Frankie Dettori as the well-fancied Emily Upjohn failed to figure.

- with AP