Viktor Hovland birdied seven of his final nine holes to overtake overnight leaders Matt Fitzpatrick and Scotty Scheffler and win the BMW Championship by two strokes at Olympia Fields.
The 25-year-old Norwegian started the day three shots behind world number one Scheffler and England’s Fitzpatrick.
But he carded a career-low nine-under 61 to set a new course record and claim a $3.6m (£2.8m) winner’s cheque.
Northern Ireland’s Rory McIlroy shot a 66 and tied for fourth at 12 under.
Hovland, joint runner-up at May’s USPGA Championship, finished at 17 under after the final round to break the course record of 62 set by Max Houma and Sam Burns earlier in the week.
“This has to be my number one [period of my career],” he told JEE News.
“I remember playing a very special round of golf in my first year on tour – I shot seven under at Torrey Pines when it was hailing and windy and raining and it’s probably the best I’ve ever played. Hit him throughout the round.
“But to shoot a 61 on this golf course and a 28 on the back nine and in those conditions, I don’t have anything that can beat that.”
The BMW Championship is the final stage of the season-ending FedEx Playoffs.
The field consists of the top 50 in the PGA Tour’s FedEx Cup standings, including the top 30 who qualify for next week’s Tour Championship finals in Atlanta.
American Scheffler will start the Tour Championship with a two-shot advantage after spending Saturday atop the FedEx Cup rankings.
Hovland is set to move up from seventh to second, with his Ryder Cup teammate McIlroy in third.
Howland’s impressive run saw him birdie three holes in a row from the 10th, pick up more shots at the 14th and 15th and move into a share of the lead with his ninth birdie of the day at the 17th.
He birdied the final hole to move to the top of the leaderboard, with Scheffler three-putting at the 17th to secure Hovland’s victory.
Fitzpatrick, whose younger brother Alex finished second on the DP World Tour earlier in the day, finished even with playing partner Scheffler’s 66 at 15 under.
Hovland added: “I was thinking if I posted a score like yesterday [65] I might at least have a chance, but it’s hard when you have a lot of guys in front of you who are really good. And playing great.
“Catch the heat on the back nine was what I had to do.”
