American Pharoah's Triple Crown bid has received a boost with two early withdrawals from the Belmont Stakes.

Carpe Diem and The Truth Or Else have been taken out leaving a field of just eight for the final leg of the Triple Crown on Saturday (Sunday AEST).

American Pharoah, a decisive winner of the Kentucky Derby and Preakness Stakes, is trying to become the first Triple Crown winner since Affirmed in 1978.

He had his final work-out on Monday at a wet Churchill Downs, pleasing trainer Bob Baffert.

"I was worried about the rain, but the track was in perfect shape," Baffert said.

"It seemed to let up a little bit when he worked. It went just as we thought."

The horse will travel to New York on Tuesday (Wednesday AEST).

Baffert is no stranger to the Triple Crown spotlight. The Hall of Fame trainer has been one win away before, and he expects the spectacle to be no different from what he faced with War Emblem (2002), Real Quiet (1998) and Silver Charm (1997).

"I know what I'm walking into," Baffert said.

"It's going to be pretty crazy.

"One thing about the horse, we know what to expect. We're not going to be overwhelmed by it because we're used to the big show."