Country House, a longshot at 65-1, won the 145th running of the Kentucky Derby after a rider's objection led to the disqualification of Maximum Security, who crossed the line first at Churchill Downs on Saturday.
It was the first time the horse crossing the line first has been disqualified.
Maximum Security, the 9/2 second-choice favorite ridden by Luis Saez, finished in an unofficial 2:03.93.
But Country House's jockey, Flavien Prat, filed a rider's objection claiming that Maximum Security veered out of his path in the final turn, and it was upheld following a lengthy review.
Code of Honor (14-1) finished second after the disqualification, followed by Tacitus (5-1) and Improbable (the 4-1 favorite).