I'll Have Another looked like just another horse at the Kentucky Derby.Until the final furlong (200m), that is.That's when the chestnut colt - sold for a paltry $US11,000 ($A10,750) and ridden by a rookie jockey hardly anyone knew, blazed past highly regarded Bodemeister to win by 1-1-2 lengths on Saturday, beating one of the deepest fields in years.I'll Have Another was the first winner in 138 runnings of the race to start from gate 19 and bided his time midfield while Bodemeister set a blister

I'll Have Another looked like just another horse at the Kentucky Derby.

Until the final furlong (200m), that is.

That's when the chestnut colt - sold for a paltry $US11,000 ($A10,750) and ridden by a rookie jockey hardly anyone knew, blazed past highly regarded Bodemeister to win by 1-1-2 lengths on Saturday, beating one of the deepest fields in years.

I'll Have Another was the first winner in 138 runnings of the race to start from gate 19 and bided his time midfield while Bodemeister set a blistering pace on a muggy, 85-degree afternoon at Churchill Downs.

"He's an amazing horse. I kept telling everybody, from the first time I met him, I knew he was the one. I knew he was good," jockey Mario Gutierrez said.

Making his Derby debut at 25, Gutierrez got his chance to ride I'll Have Another after trainer Doug O'Neill and owner J Paul Reddam happened to see him at Santa Anita in Southern California.

"I don't know if he won or not, but he really looked good in the irons to me," Reddam said.

"I said: 'We need to try some new blood'."

It was another chapter in Gutierrez's unusual route to the Derby winner's circle. He followed in his father's footsteps as a jockey, getting on quarterhorses in Veracruz, Mexico, at 14.

After a stint in Canada, he eventually started getting noticed on the West Coast, especially after winning the Santa Anita Derby last month.

"Top trainers, top owners, of course, they're not going to know anything about me," he said.

Gutierrez was largely a mystery to the record crowd of 165,307, who didn't know 15-1 shot I'll Have Another or the jockey had the right stuff until the 20-horse field turned for home.

That's when Gutierrez, who moved up between horses around the final turn, positioned his colt not far from the rail and set him down to run.

"I know my horse was reaching every single step of the way, but I wasn't going to stop riding until I was passing the wire," he said.

"That is when the horse race is finished."

I'll Have Another overhauled a tiring Bodemeister, the 4-1 favourite.

O'Neill didn't waste any time vowing I'll Have Another would go on to the Preakness in two weeks.

I'll Have Another made his way to the starting gate accompanied by his stable pony, Lava Man, another cheap purchase turned into a career winner of more than $5 million by O'Neill. The trainer has made his name predominantly in Southern California, although he's won three Breeders' Cup races.

"When you tell people you're in the horse racing game, they ask you, 'Have you won the Kentucky Derby?'" O'Neill said.

"Now I can say, 'Yes, I have, 2012.'"

A hot pace was anticipated from speedster Trinniberg, although, surprisingly, it was Bodemeister under jockey Mike Smith who bolted to the front and forced Trinniberg to take a backseat.

In the late afternoon heat, Bodemeister set impossibly fast fractions. He ran the opening quarter-mile (400m) in 22.32 seconds and the half-mile in 45.39.

"I told Mike, 'Look, if he breaks great and feels like running, we can win it," said Baffert, who was hospitalised just five weeks ago following a heart attack in Dubai.

"That's the only time I've run second where I've been happy because he ran his race."