Rory McIlroy let his lead slip as Brooks Koepka stormed to victory a the WGC Fed Ex St Jude Invitational in Memphis, his third win this season.
54-hole leader McIlroy had a one-stroke advantage heading into the final round but ended up five strokes behind the world number one on 11-under-par.
Koepka, who had been battling illness all week, shot a final-round 65 to finish three strokes ahead of fellow American Webb Simpson with Australia's Marc Leishman a shot further back in third.
English duo Tommy Fleetwood and Matt Fitzpatrick finished level with McIlroy in fourth at 11-under.
Irish Open champion Jon Rahm, who was the first-round leader, ended up on 10-under.
Koepka feels defeating McIlroy on the final day makes his latest title all the more satisfying.
"It feels really good. I knew I had to make some putts and to catch up with Rory by nine would be big.
"I played really solid. The goal was to make no bogeys and I came out bogey-free so I'm really pleased.
"To win this title against Rory was pretty special."
“It’s incredible. To look at what I've done this year, just show consistency, try to take my game to a new level and I've done that. To be up there in the FedExCup with a chance in Atlanta, that's incredible,” Koepka added.
“But to win the Wyndham Rewards is incredible. That's what you shoot for. You want to be No. 1 when the season's done and going into the Playoffs, and then to add Aon Risk Reward, it just comes from the consistency. It's incredible to look at how much you could have won today, and to do it, it's been incredible.
“This run I'm on the last couple years has been so special. I've given myself some good chances but I've just never played well in the Playoffs. I don't know what it is, whether it's just a little burnt out or what, but I haven't gotten it done.
"So this year, in a little better shape. Hopefully a week off will just kind of relax and take it easy and then get back in the swing of things.”