Rory McIlroy has opened up a golfing rivalry for the ages after his Tour Championship victory delivered a stunning $US15 million pay day as he chased down world No.1 Brooks Koepka.
McIlroy admitted his motivation to beat Koepka at the US PGA Tour's season finale was a crushing defeat to the big-hitting American at the World Golf Championships event in Tennessee in July.
But on Sunday, McIlroy pulled the rug from underneath 54-hole leader Koepka while paired with him in the final group at East Lake Golf Club in Atlanta, Georgia.
McIlroy, the 2016 play-offs winner, carded a four-under 66 to finish at 18-under-par and four shots clear of American Xander Schauffele (70).
Koepka (72) and Justin Thomas (68) shared third at 13 under.
Australian Adam Scott's 66 was the the equal low round of the day, alog with McIlroy, and lifted him to sixth place at eight under - securing a $US1.9m ($A2.8m) in FedEx Cup bonus money.
The turning point in the final round came when Koepka, who held an early one-shot lead, lost a ball from an errant tee shot at the seventh hole and made double-bogey six.
McIlroy made a timely birdie on the same hole to steal the lead in a three-shot swing and the Northern Irishman never looked back.
McIlroy said he was driven by blowing the 54-hole lead to final group partner Koepka at the WGC-Invitational in Memphis.
"Once I saw I was in the final group with Brooks, it just took me back to Memphis a few weeks ago," McIlroy said.
"It gave me that little bit of extra motivation to right some wrongs.
"Brooks went out there in Memphis and shot 65 and just basically dominated the tournament, dominated me.
"I realised if I want to become the dominant player in the world again, I need to be more like him."
With McIlroy's 17th US PGA Tour win, he moves to world No.2 and within striking distance of top-ranked Koepka.
Both are four-time major winners and their battles are shaping up to be a rivalry not seen in golf since Tiger Woods and Phil Mickelson duelled from the late 1990s to the late 2000s.
"Brooks is a great player. He's turned into a heck of a player over the last couple of years, and I definitely expect more Sundays like that between the both of us in the future," McIlroy said.
The Tour Championship win caps a stellar season for McIlroy, who was victorious at the elite Players Championship - regarded as golf's unofficial fifth major - as well as the prestigious Canadian Open.
McIlroy also appears a lock to claim a third PGA Tour Player of The Year award.
The 30-year-old also finished the PGA Tour season with top-10s in 73.7 per cent of his starts - the highest percentage for any player since Englishman Luke Donald posted the same percentage in 2011.
"I think I've given myself so many chances and to win three times is awesome," McIlroy said.
"I feel like I could have won more but to win the FedEx Cup again, to persist the whole way throughout the year, to keep giving myself chances even when I was getting knocked back, I'm very proud of myself.
"I'm going to enjoy this one tonight."
Australia's Marc Leishman shot a 67 to finish tied for 24th at two over to take home $450,500 ($A670,800).