Norway's Viktor Hovland hit a superb bogey-free seven-under-par 63 to win the Tour Championship and FedEx Cup title at East Lake in Atlanta.
Hovland led by six going into Sunday's final round but was pressed by Xander Schauffele, who shot a 62 and closed to within three strokes with six to play.
However, Hovland birdied the final three holes to win by five strokes on 27 under and collect $18m (£14.1m).
"It's pretty surreal to be standing here right now," he said.
"The gameplan before starting was middle of the green, make a lot of pars and make Xander get after it, which he did early so I had to change my gameplan a little bit."
Hovland and Schauffele had equally fast starts, both picking up four birdies in their opening six holes after a near two-hour delay because of lightning and heavy rain.
The American holed further birdie putts on the eighth, 11th and 12th holes to reduce the deficit to three as Hovland missed chances of his own but also made some crucial par putts.
It looked like the world number five's advantage may be further reduced on the 14th after he hit a poor chip but he sensationally holed a 23-foot putt to save par.
"That was just huge for momentum because two shots with four holes to go is a lot different from three shots," Hovland said.
"And after that I really relaxed."
His fifth birdie of the day came on the 16th, to end a run of nine pars, and he added two more on the 17th and 18th to seal his sixth PGA Tour victory and the biggest win of his career in the season-ending tournament.
Schauffele also had a bogey-free round as he finished on 22 under to claim the $6.5m (£5.2m) runner-up prize from the $75m (£59.5m) bonus pot. US Open champion Wyndham Clark finished third on 16 under.
World number one Scottie Scheffler, who started the week two shots ahead of Hovland on 10 under par as leader of the FedEx Cup standings, had a disappointing week and closed with a level-par 70 to finish on 11 under.
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