I'm d' mac (outside), with in-form apprentice Omar Walker aboard, holds off SIR KUNJABIHARI (Richard Mitchell) by a neck to win the seventh race for native-bred three-year-olds (non-winners of two) over 1500 metres at Caymanas Park on Wednesday. Trained by Philip Feanny, I'm d' mac won at odds of 4-1. - Colin Hamilton/Freelance Photographer

LOUISVILLE (Reuters):

Unbeaten, untested and with a temperament still largely unknown, Curlin has plenty of sceptics who claim he cannot win the Kentucky Derby. But trainer Steve Asmussen is convinced that the muscular chestnut colt will not have any problems in today's 20-horse affair despite having raced only three times.

"I do not believe the three races, or not running as a two-year-old, will be any excuse," Asmussen, the nation's top trainer in wins, told reporters at historic Churchill Downs. "I'm excited just to witness the horse, much less be fortunate enough to be able to train him."

Curlin, with Robby Albarado in the saddle, is listed as the early 7-2 favourite in the 133rd running of America's premier race. Breeders' Cup juvenile champion Street Sense is the second choice for the mile-and-a-quarter event at 4-1.

The field is wide open this year, with none of the 20 three-year-olds seen as a serious threat to become the first Triple Crown winner since Affirmed in 1978. But Curlin appears to be the mystery horse, the colt that could defy the history books and perhaps emerge as the class of the field.