Shane Lowry faded to 43rd as the left-hander Ted Potter Jr. off the chasing pack in style to capture the AT&T Pebble Beach Pro-Am and secure a second Masters appearance.
Tied for the lead with world number one Dustin Johnson thanks to a superb third round 62 at Monterey Peninsula, Potter (34) closed with a classy, three-under 69 to win by three shots from Johnson, Phil Mickelson, Chez Reavie and Jason Day on 17-under par.
Johnson was the hot favourite to take the title for the third time since 2009.
But he could only manage a level par 72 and was outplayed by Potter, who picked his shots well and scrambled for par six times out of six when he was in trouble.
Johnson (33) consistently outdrove Potter but simply made too many mistakes in a level par front nine, and it was the man they call "the Wizard" who seized his opportunity, going out in 33 before holding off all comers to clinch a cheque for $1,332,000 and a ticket to Augusta National.
After starting with a three-putt bogey, he birdied the second, fourth and sixth, then chipped in for a two at the seventh to move two shots clear before plotting his way to victory with ten successive pars.
The champion, whose only previous victory came in the 2012 Greenbrier Classic, graduated from the Web.com Tour last year after broken ankle he suffered in 2014 put him out of the game for 21 months.
"I'm sure everybody knew probably going into this tournament Dustin's probably going to win the golf tournament, so I knew I'm the underdog there," said Potter, whose caddied estimated had won close to 60 professional events between mini tours and the Web.com Tour.
"What do I got to lose, really. Just go out there and try to play the best golf I could today and see what happens. Why put more pressure on myself to say I'm playing against the world No. 1 or just go play golf."
If Johnson and the rest of the chasing pack was disappointed, the event was a case of what might have been for the Irish contenders as Rory McIlroy, Pádraig Harrington, Graeme McDowell, Paul Dunne and Seamus Power all missed the 54-hole cut.
Lowry made it, but after starting the final round tied for 16th, he fizzled out with a closing 74 to slip to tied 43rd on five-under par, earning $25,160 as Kevin Streelman and 13-handicap NFL star Larry Fitzgerald won the Pro-Am.
The Clara man produced many moments of note, but he was far from his best last night and mixed birdies at the seventh and 15th with missed greens leading to bogeys at the first, 11th, 14th and 17th.
He will be hoping for better in the Genesis Open at Riviera Country Club in Los Angeles this week where Tiger Woods will continue his comeback and McIlroy will be trying to quieten chatter about his putting at a venue where he was tied 20th two years ago.
After officially taking 38 putts at Monterey Peninsula's Shore Course in a three-over 74 on Friday, the four-time major winner admitted on Saturday that poa annua greens do little for his trust in his putting.
"I have to learn to trust my lines, especially on these poa annua greens," McIlroy said after missing the cut by two strokes on Saturday.
"I hit the ball well at Spyglass, and I scored well. I missed two greens yesterday, only missed one fairway, and I shot three-over. So that wasn't too good on the greens.
"Today, I hit some really good shots and, yeah, I just need a few putts to fall, and I think sometimes with these poa annua greens you start to get a little bit tentative with them and it just gets away from you.
"So I let the greens yesterday get into my head a little bit, and it was hard to get out of that mindset.”
Putting was no issue for Kiradech Aphibarnrat, whose decision to cancel a holiday in the Maldives paid off as he returned to the world's top 50 with a two and one win over Australia's James Nitties in the final of the European Tour's ISPS HANDA World Super 6 Perth.
The Thai (28) took advantage of a late sponsor's invitation by claiming his fourth European Tour title in the innovative event at Karrinyup Country Club.
He needed four trips up the 18th on Saturday to beat Australian Anthony Quayle in a playoff to secure the last of 24 places in the Super 6 — a series of six-hole matchplay tussles yesterday.
He then played 35 holes in all, beating Australia's Ben Eccles (1 up), Japan's Yusaku Miyazato (5 Shootout Holes), American Sean Crocker (1 up) and Australia's Lucas Herbert (1 Shootout Hole) before defeating Nitties in the final.
"It's just been an awesome week," said Aphibarnrat, now 10th in the Race to Dubai, who showed his liking for matchplay by winning the 2015 Saltire Energy Paul Lawrie Match Play in Aberdeen.
In China, Bandon teaching professional Brian O'Donovan will be asking his Mission Hills Shenzen employers for time off after he clinched one of 15 PGA TOUR Series-China cards at the Qualifying Tournament held at Mission Hills Haikou on Hainan Island.
A third round 73 left the former Douglas assistant (30) a shot outside the all-important top 15.
But he birdied the par-five 18th from 18 feet for a level par 72 in yesterday's final round to finish tied for 12th behind American Joseph Winslow on two-under and secure his playing rights for 2018.
After a one-year hiatus, the PGA TOUR Series-China resumes in March with a 14-tournament schedule, awarding Web.com Tour status to the top five money winners.