Mage swooped late to run down Two Phil's to land the 149th running of the Kentucky Derby at Churchill Downs under Hall of Fame jockey Javier Castellano in front of a crowd of 150,000.
One of the least experienced runners in the field he finished powerfully up the straight to triumph in the £2.5 million race on only his fourth start.
Two Phil's launched his bid by taking the lead entering the stretch but Mage swung eight wide on the turn and joined him with a furlong to run to score at 10-1 with Angel Of Empire taking third place
It was Venezuelan born Castellano's first Kentucky Derby victory at the 16th attempt on Mage, whose trainer Gustavo Delgado was a hugely successful trainer in Venezuela before opening a stable in Florida eight years ago. It was his first success in the race too.
Mage had earned his chance after finishing second in the Florida Derby behind Forte, the pre-race favourite who was scratched from the Kentucky Derby hours before the race by track vets due to a foot bruise.
Castellano said: "Thank you lord Jesus Christ for giving me the opportunity to win the Derby, the dream for any jockey, for any trainer, any horses. I never give up. I always try hard, do the right thing. It took me a little while to get there. I finally get it. I'm very blessed.
"Mage did it really well. He got a lot of dirt in his face, came from behind horses but turning for home he got a lot a heart. He is a little horse with a big heart."
He added: "The way he run in the Fountain Of Youth and the Florida Derby, the way he did it to finish second, I think he had a lot of potential to win the Kentucky Derby."
Forte was one of five horses to be ruled out of the Kentucky Derby since final declarations were made, the most absentees since 1936.
His defection, by order of state vets, followed a tumultuous lead-up to the race triggered by a spate of horse deaths during the Churchill Downs meet.
On Thursday Churchill Downs management suspended trainer Saffie Joseph who trained two of the fatalities, ruling his Kentucky Derby runner Lord Miles out of the Classic.
Two more horses were euthanised after running on the Kentucky Derby undercard to take the week's tally to seven and another Here Mi Song left the track in a horse ambulance.
