ARCADIA, Calif. -- Vino Rosso won the $6 million Breeders' Cup Classic by 4 1/4 lengths, drawing away from 5-2 favourite McKinzie down the stretch of a race marred by a "serious" injury to a 15-1 long shot Saturday night.

Mongolian Groom was part of the early pace in the 1 1/4-mile race that capped the two-day world championships at Santa Anita. But jockey Abel Cedillo sharply pulled up the 4-year-old gelding near the eighth pole as the rest of the field charged toward the finish line.   

"We know he's injured his left hind leg," said Dr. Al Ruggles, the on-call veterinarian.

Dr. Scott Palmer, another on-call vet, described the injury as "serious."

Santa Anita has been the site of 36 horse deaths since December. Track owner The Stronach Group rushed to implement changes to rules involving medication and training. The Breeders' Cup also beefed up its own pre-race exams and observations of Cup runners.

It was the only injury in the 14 Cup races.

A green screen was rushed onto the track to block Mongolian Groom from the view of 67,811 fans and a prime-time television audience. He was loaded onto an equine ambulance and taken to a hospital on the backstretch.

Tyler Gaffalione, aboard War of Will, turned his head back to look at Cedillo, who was right behind him along the rail.

Mongolian Groom has three wins in 17 career starts and earnings of $579,141. He was coming off a victory over McKinzie in the Awesome Again Stakes on the same track in September that earned him a berth in the Classic.

Bred in Kentucky by Calumet Farm, Mongolian Groom is trained by Ganbat Enebish and owned by Mongolian Stable, the name of Ganbaatar Dagvadorj's racing operation. His best horse was 2015 Turf Sprint winner Mongolian Saturday, who like Mongolian Groom was a 15-1 shot in the Breeders' Cup.

Winning co-owner Mike Repole called Mongolian Groom's injury "the worst part of this game."

"For us, horse safety is very, very important. Prayers for the horse. Prayers for the connections of the horse. It's got to be really, really tough. It's very sad," Repole said.

Winning trainer Todd Pletcher said he was concerned about horse safety at Santa Anita coming into the season-ending world championships.

"We were anxious, not only for running in huge races like this, but hoping everything would go smoothly and safely," he said. "Everyone took every precautionary measure they possibly could."

Four horses were scratched Saturday from Cup races after pre-race exams by vets found issues concerning enough to keep them in their barns.

Earlier in the day, protesters angered by the 36 deaths stood outside Santa Anita toting signs urging the end of the sport in California. A short distance away, industry workers feeling pressured by the prospect of losing their jobs rallied to promote racing.

Vino Rosso went off at 9-2 odds for Pletcher, who won his first Classic.

"It's one thing that was missing," Pletcher said. "It feels great."

Jockey Irad Ortiz Jr. earned a leading fourth Cup victory of the weekend that featured just three victories by favourites.

McKinzie, the 5-2 favourite, finished second for trainer Bob Baffert.

Higher Power was third and Elate, a 5-year-old mare taking on the boys, finished fourth.

Vino Rosso covered the distance in 2:02.80 and paid $11.20, $5.80 and $4.

Saturday's biggest upset belonged to 14-1 shot Belvoir Bay in the $1 million Turf Sprint. The 6-year-old mare beat the boys for a 1 1/4-length victory. She paid $31.60 to win.

Trainer Chad Brown won a leading three Cup races over the two days to move into a second-place tie for career victories with Baffert at 15.

Ireland's Joseph O'Brien made history. At 26, he became the youngest trainer to win a Cup race with Iridessa's neck victory in the $2 million Filly & Mare Turf. He beat his father, Aidan, who saddled Just Wonderful to a fifth-place finish.

Iridessa was the day's second-longest priced winner at 13-1 odds, paying $28.40 to win.

Joseph O'Brien also joined Freddie Head as the only person to train and ride a Cup winner. O'Brien won the 2011 Turf with St Nicholas Abbey before eventually growing too tall to remain a jockey.

Iridessa earned the only European victory of the weekend.

The weekend's biggest shocker occurred in the $2 million Juvenile on Friday. Storm the Court won by a neck. He paid $93.80 at 45-1 odds, the highest payout in the race's 35-year history.

In other races Saturday:

   -- Bricks and Mortar won the $4 million Turf by a head to complete a perfect season and move solidly into contention for Horse of the Year honours. He's 6 for 6 this season and has won seven in a row dating to last year.
   -- Covfefe won the $1 million Filly & Mare Sprint by three-quarters of a length as the 3-2 favourite.
   -- Spun to Run won the $1 million Dirt Mile by 2 3/4 lengths at 9-1 odds, upsetting even-money favourite Omaha Beach.
   -- 9-5 shot Mitole won the $2 million Sprint by 1 1/4 lengths for his sixth win in seven starts this year.
   -- Uni won the $2 million Mile on the turf by 1 1/4 lengths over 3-1 favourite Get Stormy.
   -- Blue Prize rallied from second-to-last on the backstretch to win the $2 million Distaff by 1 1/2 lengths, upsetting even-money favourite Midnight Bisou, who lost for the first time in eight races this year.