Aidan O'Brien arrived in Louisville from Ireland on Thursday and was at Churchill on Friday morning to watch his sixth Kentucky Derby starter, Mendelssohn, go through routine exercise the day before Derby. Mendelssohn jogged and gallop, and most importantly appears comfortable enough on the Churchill dirt track. O'Brien said Mendelssohn's rider on Friday "was very happy with the way he went over the surface."

Mendelssohn will be racing five weeks after winning the Group 2, $2 million UAE Derby by 18 1/2 lengths and will be making his third start of the year, and O'Brien believes he's bringing a fresh horse to the Derby. Mendelssohn was asked early by jockey Ryan Moore to make the lead in the UAE Derby, but seems unlikely to go to the front Saturday.

"I would imagine he'd be somewhat forward, but I didn't speak to Ryan and Ryan would decide that always," O'Brien said. "He made [the pace] in Meydan but I wouldn't be sure he'd make it here."