Three-time Kentucky Derby winning jockey Gary Stevens is to partner Johannesburg in Saturday's race and Jerry Bailey is to ride the other Aidan O'Brien-trained candidate Castle Gandolfo.

The bookings were announced by Coolmore representative Demi O'Byrne at Churchill Downs yesterday after the two colts had arrived safely at Keeneland racecourse.

O'Byrne indicated that it was O'Brien who decided which of the two top Americans rode each horse.

He said: "We are very lucky to get Gary and Jerry but in the end it was Aidan's call as to who rode what. The horses arrived at Blue Grass Airport and went directly into quarantine. How long they stay there depends on the result of blood tests."

It is understood that last year's Breeders' Cup Juvenile winner Johannesburg and Castle Gandolfo will have their only work ahead of the Derby at Keeneland tomorrow before travelling to Louisville early on Saturday. Aidan O'Brien is expected to arrive in the US tomorrow.

Godolphin's Derby hope Essence of Dubai pleased connections in aearly five-furlong workout.

The organisation's Tom Albertrani said: "It was a good solid workout and I timed him at 1 minute 1.4 seconds. He finished up strongly and galloped out very well.

"He is well within himself and is right on target for Saturday." Stable-companion Imperial Gesture, who is being aimed at tomorrow's Kentucky Oaks, also worked over five furlongs on dirt at Churchill Downs in the morning.

Take Charge Lady, unbeaten in three races this year, is 2 to 1 favourite in a field of 10.