Unheralded Derek Ernst beat England's David Lynn in a play-off to capture the Wells Fargo Championship at Quail Hollow.
Ernst, who was fourth alternate for the event, only got his place in the field due to the numerous pre-tournament withdrawals believed to be caused by the poor state of the greens.
But the 22-year-old American rookie took his chance in fairytale fashion. A brilliant birdie at the 18th secured him a spot in a play-off and a two-putt par at the first extra hole edged out 2012 USPGA runner-up Lynn, who couldn't recover from a poor tee-shot.
The two unlikely play-off contenders had benefitted from a late collapse by Phil Mickelson.
Joint overnight leader Mickelson appeared to be in control of the tournament when grinding out eight straight pars from the sixth to the 13th and then almost chipping in for eagle at the short par four 14th.
The left-hander's tap-in birdie took him to nine-under and secured a one-shot lead and a good drive at the par five 15th suggested he'd add another birdie to pull two clear.
However, Mickelson found sand with his second, failed to get up and down for his birdie and from there it all went wrong.
Up ahead on the course, Ernst hit a brilliant 184-yard approach to inside five feet and holed for birdie to post eight-under. And seconds later Lynn, who had chipped in for birdie at 16, matched that clubhouse total and round of two-under 70 after a closing two-putt par.
It meant Mickelson had to play the three closing holes - collectively known as 'The Green Mile' - in level par to win but he bogeyed 16 to fall into a three-way tie, three-putted 17 to slip one back and failed with a birdie try at 18 which would have got him into a play-off.
Mickelson's one-over 73 left him in solo third, a shot ahead of England's Lee Westwood, who was joint leader after a birdie at 10, and Sweden's Robert Karlsson.
World number two Rory McIlroy was just a shot back after the 11th hole but double bogeyed the 12th, bogeyed the 13th and eventually finished in a tie for 10th.
Ernst was completely under the radar ahead of the event having missed six of his eight cuts so far in 2013 and finished 59th and 47th in the other two.
He had been ranked a 500/1 shot by Sky Bet before Thursday's tee-off.