Most jockeys spend all winter in search of the horse they will ride in the Kentucky Derby. Javier Castellano thought he had found his Derby mount nine months ago. After Castellano guided Union Rags to a 7 1/4-length victory in the Grade 2 Saratoga Special on Aug. 15, he thought to himself “that’s my Derby horse.” He felt only stronger about it after he rode Union Rags to a 5 1/4-length victory in the Grade 1 Champagne at Belmont in October. While Union Rags will be one of the favorites for Saturday’s 138th Kentucky Derby, Castellano will be on the back of a different horse. By his own choosing, he will not ride Union Rags. Instead, Castellano will be aboard Gemologist, the undefeated winner of the Wood Memorial. Gemologist certainly has a chance to win, but he figures to be a longer price on the tote board than Union Rags, who will be ridden by Julien Leparoux. The decision Castellano and his agent, Matt Muzikar, had to make speaks to the prominent role Castellano now plays in the barn of powerhouse trainer Todd Pletcher. It also speaks to the rise to prominence of Castellano, who leads all riders through the first four months of 2012 in purse money won with $6.8 million. [KENTUCKY DERBY: Get PPs, watch analysis video, and read pre-race reports] A little bribe never hurts Castellano, 34, was aboard no fewer than five talented 3-year-olds for Pletcher during the winter. The most impressive of those was Algorithms, who destroyed defending 2-year-old champion Hansen in the Grade 3 Holy Bull on Jan. 29 at Gulfstream. Earlier that same day, Castellano won an allowance race aboard the Pletcher-trained El Padrino, on whom he would win the Risen Star Stakes. Castellano also had ridden Discreet Dancer to a pair of emphatic victories. “Sometimes it’s hard to find one, now you get on four,” said Castellano, who also had Gemologist waiting in the wings off his 3-for-3 2-year-old campaign. With Algorithms, Discreet Dancer, and Union Rags, trained by Michael Matz, all pointing to the Fountain of Youth on Feb. 26, Castellano had to decide whom to ride. On Feb. 12, two weeks before the Fountain of Youth, Castellano and Muzikar chose Algorithms, only to have that horse get hurt a few days before the race, an injury that knocked him off the Derby trail. Muzikar and Castellano admitted part of their decision was to show some loyalty to Pletcher, who has used Castellano on a more accelerated rate over the years. “It’s not always black and white,” Muzikar said. “It’s not always about which horse is better.” However, Castellano said that the way Algorithms ran in the Holy Bull, “I thought he could beat Union Rags.” The day before the Fountain of Youth, Castellano won the Risen Star Stakes at Fair Grounds on El Padrino. Perhaps that would be his Derby horse. He faltered in the Florida Derby. But on March 16, Castellano was reunited with Gemologist, a horse he had ridden to victories in an allowance race and the Grade 2 Kentucky Jockey Club – both at Churchill Downs – last fall. In a one-turn mile allowance race, Gemologist rolled to a seven-length victory over the Grade 1 Hopeful winner Currency Swap. Three weeks later, Castellano rode Gemologist again in the Wood Memorial at Aqueduct, where he would need a top-two finish just to qualify for the Derby. In the Wood, Gemologist was five wide into the first turn and three wide and about three lengths off the early pace down the backside in the Wood. He made the lead turning for home, appeared to be opening up in the stretch and repelled a late run by Alpha, who looked as though he was going to run by Gemologist. “At sixteenth pole he started waiting, waiting, waiting for horses,” Castellano said. “When he saw Alpha, he took off. That showed me he’s got a lot of potential and he needed to start putting it together, and I think he will. I was so proud the way he did it. He showed me he could go that far, and he was very competitive.” Gemologist will be Castellano’s sixth Derby mount. His first one, Bellamy Road in 2005, was his best chance. Coming off a 17-length victory in the Wood Memorial, Bellamy Road was sent off the 5-2 favorite. He finished seventh. Castellano’s four mounts since have finished 15th, 18th, 13th, and 13th. “I believe the Derby is about luck,” Castellano said. “Of course you need to have the horse, but you need to have the luck.” Castellano also has a big chance in Friday’s Kentucky Oaks as he will ride morning-line favorite Grace Hall. Castellano picked up that mount because of the success he had during the Gulfstream meet where he set a record with 112 wins, including 10 stakes victories. That certainly caught the attention of trainer Tony Dutrow, who talked the owners of Grace Hall into making a change from two-time Eclipse Award-winning rider Ramon Dominguez to Castellano following Grace Hall’s loss in the Davona Dale. “Castellano’s setting records,” Dutrow told his owners. “He’s in a zone here like nobody else. I think what is in the best interests of us is to join that guy that is white hot.” While Castellano has not usurped John Velazquez as the first-call rider for Pletcher, he has certainly received a ton of business this year. He has 28 winners from 75 mounts for Pletcher. John Velazquez is 37 for 95 in 2012 for Pletcher. Pletcher has used Castellano increasingly over the years and has enough faith in the jockey that he told him last summer not to be afraid to use his own judgment when a plan discussed in the paddock doesn’t lend itself to working out. “We talk about Plan A and the way you and I think the race is going to unfold, but when it doesn’t – which happens a lot – you got to know I’m okay with you calling an audible,” Pletcher said he told Castellano. “You’re not going to be right all the time, but you can’t always stick to exactly Plan A. Since then, it’s paid off a number of times.” Castellano hopes it pays off Saturday with his first Derby victory. “I really want to get this done,” Castellano said. “The way the story started this year with my Derby horse, it’s been like a roller coaster.”