Zenyatta came up just short in her bid for perfection.The six year old mare, with Mike Smith aboard, came up short by a nose in the $5 million Breeders' Cup Classic Saturday at Churchill Downs, her first and only defeat in a 20 race career. The winner of the Classic, Blame, held on to his lead despite a furious stretch run by Zenyatta, who now goes into retirement. Fly Down was third.Zenyatta was attempting to become the first thoroughbred in North America to go undefeated in 20 attempts.