updated 8:56 p.m. ET April 22, 2009

LOUISVILLE, Ky. - Big Brown was pulling away from the field, accelerating with every powerful stride toward the finish line in the Kentucky Derby.

The crowd of 157,770 was on its feet and cheering as the big, unbeaten, muscular bay crossed the line first, 4¾ lengths ahead of the filly Eight Belles.

Trainer Rick Dutrow Jr. was still celebrating, along with thousands of happy bettors, as Big Brown and the 19 other horses in Saturday’s race galloped out around the first turn at Churchill Downs.

It took a few minutes to sink in, but anyone watching those horses soon realized that one of them had fallen to the track.

“It’s the filly,” someone whispered. She went down about a quarter mile past the finish line.

In just a few minutes, the joy of the Derby and the promise of a new Triple Crown season were upended when Eight Belles was euthanized by injection on the track.

She had broken both front ankles and could not be saved.

“This horse showed you his heart,” winning jockey Kent Desormeaux said, “and Eight Belles showed you her life for our enjoyment today. I’m deeply sympathetic to that team for their loss.”

Big Brown did everything his owner said he would do. An explosive finishing kick put away his rivals for his fourth consecutive victory.

Video   Iso-cam on Big Brown Follow Kentucky Derby winner Big Brown on an isolated camera through the entire race. NBC Sports

Eight Belles, meantime, was attempting to become the fourth filly to win the Derby. Her owners chose to keep her out of Friday’s Kentucky Oaks so she could run with the boys in the Derby. And run she did.

Big Brown’s start from the outside post did little to hamper his charge when the field turned for home. Under the urging of Desormeaux, the 2-1 favorite cruised to an easy victory to become the seventh undefeated Derby winner. The last one was Barbaro in 2006.

That wasn’t the only reason thoughts of Barbaro were hard to ignore on this Derby Day.

The breakdown brought back memories of the 2006 Preakness, where Barbaro shattered his right rear leg just after the start. The colt was euthanized months later, after developing laminitis from the catastrophic injuries.

In two weeks, Big Brown will race in the Preakness as the only 3-year-old with a chance to become the first Triple Crown champion since Affirmed in 1978.

“We’re ready to roll,” Dutrow said.

All week, Dutrow told the world he had the best horse in the field — and the big bay colt justified every accolade tossed his way.

“I can’t describe the feeling that all of us have right now,” he said.

The colt became the first Derby winner since Regret in 1915 to have raced only three times previously. He is only the third in 60 years to win after racing in just two Derby preps — Sunny’s Halo in 1983 and Street Sense last year were the others.

In addition, Big Brown became the second winner to start from the No. 20 post. The gelding Clyde Van Dusen did it in 1929.

Big Brown covered the 1¼ miles in 2:01.82 in front of the second-largest crowd in Derby history. He paid $6.80, $5 and $4.80.

Eight Belles paid $10.60 and $6.40, and Denis of Cork, at odds of 27-1, returned $11.60.

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