American Pharoah reasserted his claim to Kentucky Derby favouritism when he won the $1 million Arkansas Derby by eight lengths before a crowd of more than 67,000 at Oaklawn Park.

Under regular rider Victor Espinoza, American Pharoah equalled the third-largest margin in Arkansas Derby history and his winning time of 1:48.52 despite being eased down was the fastest since 2003.

The win places trainer Bob Baffert and jockey Victor Ezpinoza in the box seat to add to their Kentucky Derby records at Churchill Downs on May 2.

Although the Arkansas Derby lacked serious opposition among his seven rivals, last year's champion two-year-old could not have done much more on his second outing since missing the Breeders' Cup with a foot injury.

Espinonza tracked the pace before taking control at the head of the stretch and then drawing away without effort. Late-running Far Right closed past beaten horses for a distant second.

"He's an amazing horse," said three-time Kentucky Derby winner and Hall of Famer Baffert.

"He's been a professional horse from the start. We were hoping he could do something like that.

“We're so excited about him. He's matured substantially.

Espinoza will be looking for his third Kentucky Derby success after War Emblem (2002) and California Chrome (2014).

"This is the first time I've gone into it with a horse like this. I think I'm even more excited this year.

"The way this horse runs is unbelievable. I don't feel like he's running that fast and then I look back and he's so far ahead.”

A Zayat Stables homebred, American Pharoah has won four of his five career starts with his only loss being at his two-year-old debut.

This was his third G1 win to go with his victories in the Del Mar Futurity and the FrontRunner Stakes at Santa Anita.

"I know that he is a very talented and very fast horse, but today he showed us a different dimension," Ahmed Zayat remarked. "This horse can do anything. He's brilliant."

Baffert is in with a strong hand in this year’s Derby as he also has Santa Anita Derby Dortmund among the top four qualifiers.

Louisiana Derby winner International Star and Todd Pletcher’s Blue Grass Stakes winner Carpe Diem are others at the top of the Derby list.

The Arkansas Derby victory was the second for Baffert. He won with subsequent Kentucky Derby runner-up Bodemeister in 2012.

American Pharaoh was scheduled to leave Oaklawn for Churchill Downs on April 13.