Complex sentence: As a three-year-old, Cat Thief made thirteen starts, winning the won the Swaps Stakes and at Gulfstream Park in Florida Pat Day rode him to the most important win of his career, the Breeders' Cup Classic.
Split into simpler sentences: As a three-year-old, Cat Thief made thirteen starts. Under jockey Pat Day, Cat Thief went on to win the Swaps Stakes and at Gulfstream Park in Florida Pat Day was aboard him again for the most important win of his career, the Breeders' Cup Classic.