Sierra Leone came from behind to win the Breeders’ Cup Classic at Del Mar Racetrack on Saturday, battling from near the back of the pack to overtake favourite Fierceness and avenge a series of close losses.

With jockey Flavien Prat aboard, Sierra Leone went off at 6-1 odds and was immediately playing catch-up amid the blistering early pace on the dirt track.

But he patiently worked his way up, grabbing the lead at the final turn and fending off fellow three-year-old Fierceness (5/2) down the stretch to win by a length and a half.

Japan’s Forever Young (4-1) was third in the 41st running of the year-end championships, which were held at the scenic coastal track in San Diego.

Chad Brown-trained 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,” Brown said after winning the US$7 million Classic, the richest horse race in North America.

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

Sierra Leone was at the centre of a controversial finish at this year’s Kentucky Derby, where he bumped Forever Young repeatedly down the stretch in a race won by Mystik Dan, coming home second with Forever Young third.

The stewards did not issue an inquiry although jockey Tyler Gaffalione was later fined by the Kentucky Horse Racing Commission for touching Forever Young during the race.

“The Kentucky Derby was a tough moment for everybody involved because you never know when you’re going to get there again,” Brown said.

“For him [Sierra Leone] to redeem himself and close out the year as probably the best three-year-old in a very deep division, I couldn’t be more happy for this horse. He really deserves it.”

With the win, Brown tied trainer Aidan O’Brien with 19 total Breeders’ Cup wins.

It was a disappointing race for Irishman O’Brien, who had hoped to capture his elusive first Classic with City of Troy, the three-year-old son of Justify who was running in his first race on dirt after dominating the European turf.

But it was not to be as he fell behind early and was never a force in the race, finishing eighth.

In the Breeders’ Cup Turf, which preceded the Classic, three-year-old Jayarebe collapsed on the track after the finish and was later pronounced dead from what officials called an apparent cardiac event.

“He was immediately attended to by a team of veterinary experts led by Dr Brent Cassady, but unfortunately passed away,” the Breeders’ Cup said in a statement.

“His jockey, Sean Levey, was uninjured. Our thoughts and condolences go out to Jayarebe’s connections and the many fans whose lives he touched.”

Animal rights group Peta urged a full investigation into the death of the thoroughbred and called for the release of all of his veterinary records.

“He was just three years old – not even physically mature – and there should be no reason for a healthy young horse to drop dead,” Peta senior vice-president Kathy Guillermo said in a statement.