World number 417 Adam Long birdied the final hole to capture his maiden PGA Tour title with a one-shot win at the Desert Classic in California.
Three shots off the lead overnight, the 31-year-old American, in only his sixth tour event, carded a bogey-free seven-under-par 65 to finish on 26 under.
Phil Mickelson had led the event since a 60 on the opening day and was two shots ahead going into the final round.
But he missed some short putts in his 69 to tie for second with Adam Hadwin.
When Hadwin pitched superbly to within inches of the hole at the 11th, it created his sixth birdie of the day and had put the Canadian three shots clear on the Stadium Course at the La Quinta Country Club.
But Long chipped in from the side of the green at the 15th for his sixth birdie of the day to join Hadwin at 25 under.
And despite missing a number of putts and not being at his magical best, Mickelson, who had 33 putts on the final day, compiled consecutive birdies to make all three players in the final group level with two holes remaining.
At the par-four 18th, Mickelson's long-range effort curved agonisingly wide of the cup and compatriot Long calmly rolled in a 13-foot putt to take the title.