Shane Lowry overturned a four-shot deficit at the start of the final day to win the Portugal Masters by one stroke ahead of Ross Fisher.
Three years after capturing the Irish Open as an amateur, the Irishman produced a final round of 66 at the Oceanico Victoria golf course for a 14-under-par total of 270.
The 25-year-old's victory was set up by an eagle two at the 11th after his approach landed a foot short of the hole and hopped in.
After birdies at the 15th and 17th, Lowry got himself in a spot of bother after driving into sand and bogeying the last for a 66.
Fisher, though, failed to force a sudden-death play-off after also finishing with a bogey, coming home with a 70.
"I can't explain how I feel now to be honest. It's a dream," said Lowry, who is only the second player to win on the European Tour as an amateur and a professional after Spain's Pablo Martin.
"I've won such a big tournament, such a prestigious event. I'm over the moon. It was like playing in Ireland [given the fans' support], it was great."
Former US Open champion Michael Campbell was third, his highest finish in four years, with a 273 with overnight leader Austrian Bernd Wiesberger, another shot behind.