The 4-year-old filly is racing's most prominent undefeated horse in several years.

An undefeated horse was going up against an undistinguished field.

Quickly Showed Speed "With an undefeated horse," the trainer said, "you have to hold your breath.

If both colts run in the Derby, it will be the first time an owner will have started two undefeated horses in the race.

Barbaro's win made him only the sixth undefeated horse to win the Kentucky Derby.

After all, the back of their undefeated horse is a valuable part of this valuable animal's anatomy.

This is no small task, even for an undefeated horse that has overcome a near-death accident and the stigma of his plebeian roots.

And for any undefeated horse, there is always that first loss.

In 1977, Seattle Slew became the only undefeated horse to sweep the series.

He became the sixth undefeated horse to come into the Kentucky Derby and leave that way.