Ted Potter Jr. outplayed the world's No. 1 player and held off everyone else to win the AT&T Pebble Beach National for his first victory since a broken ankle almost ended his career.
After flirting with a 59 on Saturday, Potter got off to another hot start in the fourth round, birdieing four of his first seven holes.
Left-handed Potter, who was chasing his first PGA Tour win since 2012 after a season spent on the secondary Web.com Tour past year, was semmingly unfazed by his final round pairing with the world number one as he shot into the lead on 17 under with four birdies in a stretch from the second to the Par 3 seventhwhere he pitched in for a two. He needed one more birdie to post just the 10th sub-60 round ever on the US PGA Tour.
Potter finished at 17-under 270 for his second PGA Tour win, after his previous success in 2012.
The victory was a remarkable comeback by Potter, who incurred a fractured right ankle in a "freak accident" in 2014 when he slipped on a path.
Overnight co-leader Johnson made four bogeys in his even-par 72 to blow his chances for an 18th PGA Tour title and ended tied for second with fellow Americans Phil Mickelson and Chez Reavie and Australian Jason Day on 14-under.
The left-hander played on the Web.com Tour a year ago to regain his PGA Tour card after time out with a broken ankle. He was tied with Troy Merritt who signed for a 69 at Monterrey Peninsula. Johnson was quick out of the blocks with an eagle at the par-five second hole.
But things got tougher coming in, with bogeys at 10, 12 and 17 before he regained a share of the lead with his closing birdie.Putting troubles derailed Rory McIlroy's first Pebble Beach National Pro-Am bid as the Northern Ireland star failed to make the cut.
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