After only two years of existence, the world's richest thoroughbred race is establishing a tradition: An implausible horse will win it.

The country's four best colts were supposed to settle the horse of the year title in today's Breeders' Cup Classic at Aqueduct, but Proud Truth upset them all. Rallying from last place, the colt outran Gate Dancer in the stretch to win the $3 million event.

But the 3-year-old had to share the glory on this day of seven rich championship races at Aqueduct. Perhaps the most brilliant performance of the afternoon was that by the English filly Pebbles, who was stopped cold on the final turn but still accelerated powerfully to win the $2 million Breeders' Cup Turf. She justified the claim of some Europeans here that she is the best racehorse in the world.

The Breeders' Cup also was a triumph for trainer Wayne Lukas and owner Eugene Klein. They ran one-two in the Distaff and the Juvenile Fillies, winning with Life's Magic and Twilight Ridge.

It was a big day for California, too. In addition to Lukas' victories, two other Western-based colts won today: Tasso in the Juvenile and Precisionist in the Sprint, with a brilliant performance in 1:08 2/5.

Jockey Jorge Velasquez was the riding star, with two victories, one second and one third. Often eclipsed by some of his more flamboyant colleagues, Velasquez said after his flawless ride aboard Proud Truth, "This is one of the proudest moments of my life. What a race! What a horse! I'm so happy."

Every result of the day was logical and predictable until Proud Truth's victory. Owner John W. Galbreath's colt had been soundly beaten in the Kentucky Derby and then was knocked out of action with a leg injury. When he returned to competition last month, he won both his races but didn't look particularly impressive. Against established stars such as Chief's Crown, Gate Dancer, Track Barron and Vanlandingham, he looked overmatched.

And, indeed, for much of the Classic he didn't look like a contender. Track Barron and Vanlandingham went out to contend for the early lead and -- as has happened in their previous meetings this year -- they raced each other into defeat. They set a swift pace of :46 4/5 for a half mile and 1:11 for six furlongs, while Chief's Crown stalked them and the stretch-runners continued to bide their time.

On the turn, everybody started to move. Chief's Crown moved up outside the leaders, Turkoman accelerated on the rail, but it was Gate Dancer who momentarily looked as if he were strongest of all.

"I wanted to wait as long as possible in a race like this," jockey Chris McCarron said. "Then he made a hell of a run at the top of the stretch."

Gate Dancer had been disqualified from second place in last year's Classic for lugging in through the stretch, but today he was running straight and true and strongly. He opened a 1 1/2-length advantage early in the stretch, and looked like a winner to most people in the crowd of 42,568.

But Velasquez was waiting to make the very last move with Proud Truth. He had saved ground around the turn, angled to the outside and accelerated strongly. His task wasn't easy because Gate Dancer was in the process of running his final quarter mile in 24 seconds flat. But Proud Truth collared him in mid-stretch, and won a head-bobbing photo finish as he covered the 1 1/4 miles in 2:00 4/5.

Turkoman was four lengths farther back, and Chief's Crown faded to be a badly beaten fourth.

If the result wasn't quite as shocking as Wild Again's 31-to-1 upset last year, it was surprising enough. Proud Truth paid $16.80, $6.60 and $4.60. Gate Dancer returned $4.20 and $3.20 and Turkoman paid $6.60 to show.

But the result came as no surprise to trainer John Veitch. He maintained all last winter that Proud Truth had the makings of a classic horse, and he said, "I had great confidence in him. He might have been a shorter price if he'd won by four or five lengths last week, but Jorge rode him to a 'T' last week, just as he did today. This was as good a field as you'll ever see in racing. I have to think Proud Truth is the best horse in the country."

Fans of both Pebbles and Precisionist might give Veitch an argument. Only in the Breeders' Cup is it possible that the winner of a $3 million race might not have been even the best performer on the day's program.