Ridden by Javier Castellano, Gemologist held off the fast-finishing Alpha to win by a neck and assure himself of a place in the big three-year-old classic at Churchill Downs on May 5.
"When I asked him, he took off again," Castellano said. "I like that. I was concerned when Alpha was closing because my horse was just looking around at the crowd."
The Todd Pletcher-trained Gemologist is now unbeaten after five starts and his latest performance is sure to make him one of the favourites after some of the leading contenders were beaten in the key lead-up races.
Union Rags, whose performances had generated a lot of buzz, could only manage third place in last week's Florida Derby – won by Take Charge Indy - while last weekend's Louisville Derby was won by 99-1 outsider Hero Of Order, who was not even entered for Kentucky.
There was another surprise on Saturday when Creative Cause was narrowly beaten by I'll Have Another in the $750,000 Santa Anita Derby.
I'll Have Another held on in a ferocious sprint to the wire to win by a nose.
"I saw Creative Cause come up on the inside and I thought for a split second, running second in the Santa Anita Derby is pretty freaking good," said Doug O'Neill, trainer of I'll Have Another.
"Creative Cause coming up on the inside definitely gave me a scare, but our horse fought on. He's doing so good. Hopefully, he comes out of this good and if he's 100 percent, it's on to Louisville."
Mike Harrington, the trainer of Creative Cause, said he had lost no confidence in his horse and was also heading to the Kentucky Derby with him.
"This will set him up," said Harrington. "He ran hard. It didn't hurt him. He's still got a lot left in him.
"Maybe the other horse had to run too hard to beat him. We won't know for four weeks."