For months, River Keen's successes have been regularly interpreted as flukes. How good can a horse be if he reached the age of 6 without distinction and started his 7-year-old season in claiming races?

Today, River Keen emphatically answered that question: He's one of the best in America. The veteran scored a decisive victory in the $1 million Jockey Club Gold Cup at Belmont Park, finishing 3 1/4 lengths ahead of Behrens, who had been considered the leading candidate for the horse of the year title.

The horse's emergence as a star is probably the greatest feat in a remarkable year for trainer Bob Baffert. Although he is known for developing precocious young horses, Baffert claimed River Keen for $100,000 last December, trained him to win a stakes at Hollywood Park in July and then captured the Woodward Stakes at Belmont last month. Despite those achievements, the horse was dismissed at odds of 12 to 1 today, partly because he had no previous form over a sloppy racetrack, partly because he had been ailing from a foot injury and partly because of Behrens's lofty reputation.

Jockey Chris Antley put River Keen in contention immediately, chasing the pacesetter, Back Ring Al. Behrens had been expected to be in a similar position, but he wasn't responding to jockey Jorge Chavez's exhortations.

When Back Ring Al tired abruptly on the backstretch, River Keen and Almutawakel both shot past the leader. The two horses had battled each other to the wire in the Woodward, but today Almutawakel couldn't stay with his rival.

As River Keen opened a clear lead on the turn, the fans at Belmont looked to see if Behrens was going to launch a challenge. But even though he is a proven mud-runner, he couldn't threaten today, and barely got up for second place as River Keen drew away to cover the 1 1/4 miles in 2:01 2/5.

Trainer James Bond, who had exuded confidence all week, seemed mystified by Behrens's performance.

"He just couldn't get untracked," Bond lamented.

A victory by Behrens would have solidified his status as the favorite for the Breeders' Cup Classic at Gulfstream Park next month. The Gold Cup result has elevated the status of another Baffert colt, General Challenge, who is the last horse to defeat River Keen.

Baffert did suffer one disappointment today, when his champion filly Silverbulletday lost the $500,000 Beldame Stakes to Beautiful Pleasure.

Silverbulletday came into the Beldame with a 14-for-16 career record, but she has rarely found herself in such a difficult spot as she did today. Not only was she facing older rivals for the first time, but one of her foes, Beautiful Pleasure, was a mud-lover who appeared to be the lone front-runner in the field of five. She made full use of that tactical advantage.

Jockey Jorge Chavez, always an aggressive rider, hustled Beautiful Pleasure from the gate and opened a clear lead immediately. Jerry Bailey, aboard Silverbulletday, understood the tactical situation and kept his filly within striking distance, but Silverbulletday's forte is her mid-race acceleration, not raw early speed.

After zipping a half-mile in 45 3/5 seconds and three-quarters of a mile in 1:09 1/5, Beautiful Pleasure opened a commanding five-length lead. Silverbulletday made a run on the turn, but couldn't threaten, and the winner drew off to score by 4 3/4 lengths.

In the day's other important Breeders' Cup prep, Surfside out-dueled Darling My Darling in the stretch to win the Frizette Stakes for 2-year-old fillies.