ELMONT, N.Y., OCT. 27 -- The most dramatic moment of the Breeders' Cup -- the stretch battle between the mare Bayakoa and the filly Go for Wand -- turned into one of the most stunning tragedies in racing history today.

As a national television audience and a packed grandstand at Belmont Park watched in horror, Go for Wand broke her right front ankle, crumpled to the ground and was destroyed minutes later.

The two had been racing head and head since the start of the $1 million Distaff, and in midstretch Go for Wand had her head in front. Glory was within her reach: If she won, she likely would be voted horse of the year.

There was no warning for what happened. "She was going great," jockey Randy Romero said. "She'd never taken a bad step in her life. And then she just snapped her leg off."

It was a moment that rendered insignificant almost everything else that happened on this day at Belmont -- even though it was a day marked by drama that otherwise would have been memorable.

Unbridled won the world's richest race, the $3 million Breeders' Cup Classic, with a magnificent ride by jockey Pat Day. After breaking from the seemingly disastrous No. 14 post position, Day managed to get to the rail, moved inside the field on the turn, squeezed between the two leaders in the stretch and beat long shot Ibn Bey by a length.

In the Sprint, the much-acclaimed European speedster Dayjur was 40 yards away from victory when he jumped over a shadow cast by the top of the Belmont grandstand and lost by a neck to the Maryland-bred filly Safely Kept.

But that race was marked by disaster too when the colt Mr. Nickerson dropped dead of an apparent heart attack in midrace, throwing rider Chris Antley, who broke his right collarbone. Jockey Jose Santos was spilled from the horse Shaker Knit, who fell over Mr. Nickerson, but Santos got off the ground to win both 2-year-old races on the card, with the colt Fly So Free and the filly Meadow Star.

And there was another remarkable comeback by a jockey when 54-year-old Lester Piggott, returning to the saddle after a year's jail sentence for tax evasion, rallied from last place to win the Mile aboard the Irish colt Royal Academy.

But even before the seventh Breeders' Cup, the Distaff had been the most eagerly anticipated event of the day. While the Classic, the nominal main event, was devoid of genuine stars, there were two in the 1 1/8-mile race for fillies and mares.

Go for Wand had been the champion of her generation as a 2-year-old last year and had been even more brilliant at 3. Many experts thought she would have been able to beat males in the Classic.

When the stretch-running filly Gorgeous was withdrawn from the field Friday, the Distaff became a virtual match race between two speedsters, neither of whom could afford to let the other get away. So they raced abreast of each other from the start, going easily for the first half-mile in 46 2/5 seconds.

They matched strides as they raced around the turn and into the long Belmont stretch, and the 51,236 fans in attendance knew they were witnessing a classic. Laffit Pincay Jr. aboard Bayakoa, and Romero aboard Go for Wand, were asking the fillies for everything they had now, and Go for Wand was in front one-sixteenth of a mile from the wire. "She was determined, and she was going to win this race today," Romero said.

Then it happened.

Go for Wand took a bad step, then took another and went down suddenly, catapulting Romero over her head. Bayakoa was left alone in front, and would cross the finish line 6 3/4 lengths ahead of runner-up Colonial Waters.

But nobody was watching the winner. All eyes were on Go for Wand, who rose awkwardly to her feet, staggered across the track on three legs and collapsed by the outside fence, just yards from the winner's circle.

An outrider dismounted and cradled the filly's head, waiting for the arrival of the veterinarian and the grim ritual that would follow. Security guards pulled a blue screen in front of the prone animal.

Even the most hardened racetrackers were crying when veterinarian Neil Cleary arrived and injected into the filly's neck a barbiturate that would put her out of her misery. He said later the filly "suffered a major breakdown in her right front ankle. She had a compound injury. She ruptured ligaments in her ankle and suspensory apparatus."

Trainer Billy Badgett and his new bride, Rose -- who were looking forward to their honeymoon after the Breeders' Cup -- were racked with sobs as they watched. Nearby was one of the somberest winner's circle ceremonies ever held. Trainer Ron McAnally had scored a great triumph, but he said, choked with genuine emotion: "I can hardly talk right now. It's terrible when something like this happens."

Most observers here agreed that there was no blame to be cast for this misfortune, and that nothing was wrong with the Belmont racing strip, even though two horses had broken down here Friday before the disasters today, and even though this was the place where the great filly Ruffian broke down and was destroyed in 1975.

McAnally said: "Belmont has always been a safe track, and I couldn't see anything wrong with the condition of it," he said. "It's part of racing. . . . They {horses} give their lives for our enjoyment."