Viktor Hovland birdied seven of his final nine holes to roar past overnight leaders Matt Fitzpatrick and Scottie Scheffler and win the BMW Championship by two strokes at Olympia Fields.
The Norwegian, 25, began 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 the $3.6m (£2.8m) winner’s cheque.
Northern Ireland’s Rory McIlroy shot 66 to finish fourth on 12 under.
Hovland, joint runner-up in May’s US PGA Championship, finished on 17 under after a closing round that broke the course record of 62 set by Max Homa and Sam Burns earlier in the week.
“It has to be my number one [round of his career],” he told Sky Sports.
“I remember playing a pretty 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 that’s probably the best I’ve ever struck it throughout a round.
“But to shoot 61 and shoot 28 on the back nine at this golf course and under the circumstances, I have nothing that beats that.”
The BMW Championship is the penultimate round of the season-ending FedEx play-offs.
The field comprises the top 50 in the PGA Tour’s FedEx Cup ranking, with the top 30 qualifying for next week’s Tour Championship finale in Atlanta.
American Scheffler will begin the Tour Championship with a two-shot advantage after finishing the week top of the FedEx Cup ranking.
Hovland is poised to jump from seventh to second, with his Ryder Cup team-mate McIlroy third.
Hovland’s stunning run saw him birdie three holes in a row from the 10th, pick up more shots on the 14th and 15th and move into a share of the lead with his ninth birdie of the day on the 17th.
He birdied the final hole to move top the leaderboard, with Scheffler three-putting the 17th moments later to all but secure Hovland’s victory.
Fitzpatrick, whose younger brother Alex finished second on the DP World Tour earlier in the day, matched playing partner Scheffler’s 66 to also finish on 15 under.
Hovland added: “I was thinking if I post a score like I did yesterday [65] I could at least have a chance, but it’s hard when you have so many guys in front of you that are really good and playing awesome.
“Catching heat on the back nine was what I had to do.”