Although Zenyatta (top) and Rachel Alexandra never raced against each other, their impact on the sport of horse racing certainly constitutes a rivalry. Both females, they dominated the sport in 2009 and 2010; Rachel Alexandra won Horse of the Year in 2009, with Zenyatta earning runner-up only to win the following year. Rachel Alexandra is one of the few female horses to win a leg of the Triple Crown, the Preakness in 2009, while Zenyatta began her career 19-0 and is the only female to win the Breeders' Cup Classic.