ARCADIA, California (AP) — The Breeders’ Cup got off to a chaotic start on its second day, with a rare disqualification in the opening race and a horse euthanised with a broken leg at Santa Anita.

The US$2 million Juvenile Fillies went from strange to tragic over several minutes on Saturday. The DQ was announced after a green screen went up in a spot approaching the final turn to shield injured Secret Compass from the crowd.

“When you lose a horse like that, it just took all the wind out of our sails,” Hall of Fame trainer Bob Baffert said. “I’ve never had something like that happen on a big day. We’re all still in shock.”

Ria Antonia finished second but was declared the winner of the 1,700-metre race after She’s a Tiger was disqualified by the stewards.

They ruled that She’s a Tiger and Gary Stevens drifted out late, bumped Ria Antonia and Javier Castellano, slowing her momentum.

“I had gotten by Gary but when he came in to me, he bumped me off-stride,” Castellano said.

Stevens, who won the US$2 million Distaff with Beholder on Friday, said the stewards had a tough call.

“The stewards made their call and I wouldn’t disagree with that,” he said.

It was the first DQ of a winner since the inaugural 1984 Juvenile Fillies race in which Fran’s Valentine won and later was placed 10th.

“This is heartbreaking,” said Jeff Bonde, who trains She’s a Tiger.

“If that horse changes course and doesn’t make contact, you say, ‘OK, leave it up,'” said Jeremiah Englehart, who trains Ria Antonia. “But once you make contact it has to come down.”

Running third at the time, Secret Compass’ front legs collapsed, slamming jockey John Velazquez hard into the dirt. Baffert’s two-year-old filly was euthanised after sustaining a lateral condylar fracture, according to on-call veterinarian Dr Wayne McIlwraith.

“It is the worst type of injury we get, unfortunately,” he said.

Velazquez was to ride in all nine Breeders’ Cup races, but he was replaced by other jockeys.