Princess of Sylmar, a 38-1 outsider, won Friday's $1 million Kentucky Oaks in a major upset that left trainer Todd Pletcher with a real chance of completing one of American racing's most prestigious doubles.
Pletcher has five runners in Saturday's 139th Kentucky Derby and his chances of victory were marginally improved when the feature race was reduced to a field of 19 runners, one less than capacity, following the scratching of longshot Black Onyx.
A rank outsider at odds of 50-1, Black Onyx was withdrawn from the mile and a quarter classic at Churchill Downs after connections discovered a chip on his left front ankle on the eve of the race.
Trainer Kelly Breen said his colt was not lame and trained without any problems on Friday morning but was scratched as a precaution when X-rays showed he had a non-displaced chip.
"He actually looked pretty good training this morning," Breen said. "But he was, just like anyone else, having a bad day, whether he wrenched his ankle or slept on it wrong."
Black Onyx's scratching came too late for Fear the Kitten to take his place in the first leg of the coveted Triple Crown.
Fear the Kitten was listed as the first alternate if any of the 20 confirmed runners scratched before 9 a.m. ET (1300 GMT) but Black Onyx was not withdrawn until after the deadline.
Black Onyx had been drawn to start from pole position one, a notoriously awkward barrier which has not produced a Derby winner in more than a quarter of a century.
But race officials said the stall would remain open and the remaining 19 entrants would start from their assigned positions in a race which is looming as one of the most open in decades with at least four horses vying for favoritism.
Florida Derby winner Orb was installed as the early 7-2 favorite following Wednesday's pole-position draw, just ahead of the unbeaten Verrazano (4-1), one of Pletcher's five runners.
But when the markets opened on Friday, Revolutionary, yet another horse from Pletcher's stable, was promoted to the top of betting charts, level with Goldencents, at odds of 5-1.
Orb drifted back to 6-1 while Verrazano was rated an 11-1 chance as he bids to become the first horse since Apollo in 1882 to win the Kentucky Derby after not racing as a two-year-old.
Pletcher had four of the 10 starters in the Oaks and duly completed the first leg of the Kentucky double but not with the filly most people expected.
Princess of Sylmar, ridden by Mike Smith, defied her long odds to storm up the center of track after passing the iconic Twin Spires and win the three-year-old fillies classic.
Beholder finished a close second ahead of Unlimited Budget and the 3-2 heavy favorite Dreaming of Julia, both trained by Pletcher.