The 'Rock' was beaten by a length by Domedriver, despite a typical late burst.

But far worse was the death of Landseer, the French 2000 Guineas winner, who broke his right leg at the back of the 14-man field and was killed.

Chief Breeders' veterinarian Larry Bramlage said Landseer broke the cannon bone below his right knee but tried to keep running.

"This was a really bad one," Bramlage said.

Landseer jockey Edgar Prado, who was unharmed despite the fall, said the fall could have been much worse.

"It's terrible for that horse. It's the sad side of the story," said Prado.

"It happened so quick. Stepped in a hole, I couldn't tell. He was in a full run at the time. I had to pull him up."

'Rock' started from the No. 10 post and went to the back, then waited too late to make a charge.

Zipping past rivals with every-stride, the 'Rock' could not catch the French horse at the finish line.

Domedriver won in one minute 36.92 seconds with 'Rock' second and Good Journey third.

"I waited and waited and she had a great finish."

Rock of Gibraltar, co-owned by Manchester United manager Sir Alex Ferguson, had won seven races in a row dating to the Grand Paris Criterium a year ago.

The three-year-old colt had won each of his five starts this year, all Group I races at a mile.

Among his triumphs were the English and Irish 2000 Guineas, the Sussex Stakes and the Prix Moulin at Longchamp.

O'Brien elected to make 'Rock' a favourite in the mile rather than run him in the Classic, where a victory over Kentucky Derby and Preakness winner War Emblem would have put him in contention for Horse of the Year honours.