Before long, his contract was sold to another stable owner, a common practise at the time, and Guerin began his career as a thoroughbred horse racing jockey in 1941 at sixteen at Narragansett Park near Pawtucket, Rhode Island.

Riding for a top stable proved to be Guerin's big break as a year later he was the United States' leading apprentice jockey.

Known for his cool head and steady hand, Guerin was hired by cosmetics magnate Elizabeth Arden to ride for her Maine Chance Farm.

There, working with another future Hall of Fame trainer, Bill Winfrey, Guerin scored numerous important victories, notably with Champion fillies Bed o'Roses and Next Move.

For the final prep race leading up to the Kentucky Derby, American fans for the first time were able to watch the live telecast of the Grade 1 Wood Memorial Stakes.

Through the new type of personalized racing coverage that began introducing jockeys to a nationwide audience, NBC broadcaster Win Elliott interviewed Guerin after he rode the still-undefeated Native Dancer to victory.