Jon Rahm beat Dustin Johnson on the first hole of a play-off in a dramatic climax to the BMW Championship at Olympia Fields in Illinois, Chicago.
Spaniard Rahm, 25, looked set to be crowned champion after a bogey-free six-under 64 left him on four under.
But Johnson, who won last week by 11 shots, birdied the 15th and holed a 43-foot putt on 18 to force a play-off.
Rahm then holed an even longer putt on the same green in the play-off while the American's effort finished short.
"I still can't believe what just happened the last hour of play," Rahm said.
"That stretch of waiting for DJ, him making the putt, going in the play-off, me making the putt, then trying to stay mentally in it just in case he made the last putt. It's been a rollercoaster, but so much fun."
Rahm came from three shots behind going into the day after Johnson was tied for the lead with Japan's Hideki Matsuyama heading into Sunday's round.
The Ryder Cup player made back-to-back birdies at 15 and 16 in a sparkling round to set the clubhouse target.
His only dropped shot of the weekend was a one-stroke penalty for picking up his ball without having marked it on Saturday.