Whittingham trained several champions, including American Horse of the Year honorees Ack Ack, Ferdinand, and Sunday Silence. Among others, he trained Daryl's Joy, champion New Zealand two-year-old, winner in Australia wfa championship W S Cox Plate, Victoria Derby, Oak Tree International (USA), Cougar II, the 1972 U.S. Champion Turf Horse, Kennedy Road, the 1983 Canadian Horse of the Year, and for a time, Exceller. He also trained the champion daughter of Affirmed, Flawlessly. His horses were named Champion Female Turf Horse on four occasions. In 1986, at the age of 73, he became the oldest trainer to win the Kentucky Derby, then won the prestigious race again three years later. Both Derby-winning horses went on to win the Breeders' Cup Classic.