Bill Haas captured the FedEx Cup in Atlanta after beating Hunter Mahan in a play-off at the Tour Championship.
The Americans were tied on eight under after 18 and then shared pars on the first two extra holes before Haas parred the third as Mahan made bogey.
Luke Donald, runner-up last year, finished third in the race for the $10m (£6.4m) prize after a one-under-par 69 to end on seven under.
Donald tied for third in the Atlanta event with Aaron Baddeley and KJ Choi.
The Englishman carded four birdies, including a two on the last, but fives on four, 10 and 12 checked his progress.
He said: "Every shot counts, especially in this last tournament. At least I gave myself a chance with that birdie at the last."
The world number one earns a $1.8m (£1.2m) prize for his efforts but winner Haas takes home $11.4m (£7.4m) for clinching the season-ending Tour Championship as well as the FedEx Cup.
The 29-year-old had looked to have blown his chances of victory at the second play-off hole.
He found a bunker with his tee shot and then water with his second, but a shallow enough lie allowed him to play the ball from its resting place and he superbly pitched to within three feet and halved the hole in four.
Mahan found the greenside bunker in the third play-off hole and then allowed his escape to run 15 feet past the hole.
Haas, putting from the back fringe of the green, rolled his ball just four feet past and, after Mahan missed, he found the centre of the cup to clinch the win.
The North Carolina man entered the 30-player event 25th in points but finished on top, 15 points ahead of American Webb Simpson, who led entering the tournament.
The champion admitted at the post-round presentation he had no idea upon holing his final putt that victory brought with it the FedEx Cup bounty.
On his escape at the 17th, Haas said: "The second shot, I actually thought I hit a pretty decent shot, I just overhit it a little and maybe pushed it a bit.
"I got an unbelievably fortunate lie, it was basically a bunker shot and it was all or nothing. There was a bit of luck involved - I got some spin on it, I didn't know that - I was very lucky.
"I hung in there, I was very fortunate and it's pretty unbelievable."
Englishman Justin Rose, who won the BMW Championship in Chicago last week, finished fifth in the FedEx Cup standings.