Heath Slocum rolled in a 21ft putt to par the 18th and win The Barclays by one shot at Liberty National.
Slocum began the day four shots off the pace but jumped into contention when he holed from 158 yards for an eagle at the fifth hole in New Jersey.
Sharing second place were Tiger Woods, Ernie Els, Padraig Harrington and Steve Stricker, who came to the final hole level with Slocum.
But he missed out on forcing a play-off when his 10ft par putt trickled past.
The tournament is the first leg of the four-event FedEx Cup play-off series, where the top 125 players in the Cup standings are whittled down to a final 30 by three play-off tournaments in September.
Woods came into the weekend leading the Cup standings, with Slocum, ranked 124th, the second-lowest ranked player to qualify for the tournament.
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Not too many golf courses that you misread putts that badly
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But the 35-year-old now heads into next week's Deutsche Bank Championship ranked third following his first PGA Tour victory since 2005, earning him $1.35m (£830,905) in the process.
"My fate was not in my own hands," said Slocum, who was told by his wife that he had just qualified for the Liberty National last Sunday.
"I came in with the attitude that I've got nothing to lose and I'll let it hang out and play the best I can."
Both Slocum and Stricker found the sand from their tee shots at the 18th, with neither player able to reach the green in two shots.
A play-off looked certain until Slocum nailed his putt for par, heaping pressure on Stricker, whose effort rolled to the left of the hole.
"I'll remember that for the rest of my life," said Slocum.
"When I hit the drive I was a little concerned," he said. "I putted beautifully all week so if I just gave myself a chance, I felt like I can make one."