Bayern has won the Breeders' Cup Classic by a nose, surviving a stewards' inquiry prompted by multiple horses bumping near the start of the race.

Trainer Bob Baffert had to wait, along with a crowd of 61,114 at Santa Anita, to confirm he had finally won North America's richest race after failing in 12 previous tries.

The Hall of Fame trainer counts three Kentucky Derbys on his record but the $US5 million ($A5.41 million) Classic.

"It's been so long waiting, I was like, 'Lord, you can't take it away from me now,"' Baffert said.

"I couldn't breathe the last 20 yards."

Bayern beat English horse Toast Of New York with California Chrome third.

Shared Belief, the 5-2 favourite, was knocked off his game at the start and finished fourth, ending his undefeated streak at seven.

The stewards' inquiry involved the first four finishers.

Bayern, with Martin Garcia aboard, came over sharply on Shared Belief out of the starting gate.

That forced Shared Belief into Moreno, with V.E. Day getting squeezed. Several strides later, as the horses were scrambling to settle in for the run past the grandstand, Toast of New York smacked Moreno.

Out of the chaos, Bayern emerged with the lead, appropriate since he is usually the fastest horse away from the gate.

Bayern's two previous biggest wins of the year were in the Haskell Invitational and Pennsylvania Derby.

He missed the Kentucky Derby and finished ninth in the Preakness. He turned the corner with an impressive win in the Woody Stephens on the Belmont Stakes undercard, starting a run of four stakes wins in his last five starts.

Bayern's victory more than likely denies California Chrome champion three-year-old honours for the season and places him squarely in the running for Horse of the Year.