LONDON (REUTERS) - Justify won the 144th running of the Kentucky Derby at Churchill Downs in Louisville on Saturday (May 5), becoming the first horse since Apollo in 1882 to win the 'Run for the Roses' without a start as a two-year-old.

Unfazed by the sloppy track on a rainy Derby day, the 5/2 favourite rocketed out of the gate and was neck and neck with longshot Promises Fulfilled before jockey Mike Smith pushed the Chestnut colt into gear to record the comfortable win and break the "Curse of Apollo".

"It will take a horse like him to break that curse and just wow, he's just something else," said Smith, who also won the race in 2005 on Giacomo.

"He's got unbelievable talent and then he's got a mind to go with it. For such a young horse he is just so big and talented," he added of Justify, which has won all four of its starts.

Good Magic finished second in the first leg of US thoroughbred racing's Triple Crown series for three-year-olds, with Audible third.

The victory is the fifth for Justify trainer Bob Baffert, who also trained 2015 Triple Crown winner American Pharoah.

"He was doing it easy," Baffert said. "Him and American Pharoah and Arrogate, these horse are cut different ... I rank him up there with my top ones."

The win marks the sixth consecutive year where the favourite has won the race despite this year's field being seen as the most competitive in recent years.

Mendelssohn, the Aidan O'Brien-trained colt looking to be the first European-based horse to win the Derby, collided into other horses shortly after the break and never recovered, finishing last.

The win came on the rainiest day in the race's history with nearly three inches falling on the dirt track prior to the race, though the wet weather did little to dampen the enthusiasm of the 157,813 in attendance.