McIlroy, the 2016 Playoffs winner, carded a 66 at the par-70 East Lake Golf Club in Atlanta to finish at 18-under-par and four shots ahead of American Xander Schauffele (70).

Justin Thomas (68) and Brooks Koepka (72) shared third at 13 under.

Queenslander Adam Scott's 66 was the equal low round of the day and lifted him to sixth place at eight under – securing him US$1.9m (AU$2.8m) in FedExCup bonus money.

Four-time major winner McIlroy was ecstatic to have defeated the big-hitting Koepka, who overcame McIlroy's 54-hole lead to win the WGC-Memphis event last month, and collect the biggest first prize in the sport.

"Going up against the No.1 player in the world today (Koepka), he got one over on me in Memphis, and I wanted to try to sort of get some revenge today," said McIlroy, who moves to No.2 on the world rankings.

"To play like that alongside Brooks and win the FedExCup, it's awesome. It's amazing how different things can be in a year."

The Tour Championship win caps a stellar season for the Northern Irishman, who was victorious at the elite Players Championship – which is regarded as golf's unofficial fifth major – as well as the prestigious Canadian Open.

RIGHT: Scott shot the equal low round of the day and finished sixth. PHOTO: Sam Greenwood/Getty Images.

McIlroy 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 percent 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 FedExCup 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."

The turning point on Sunday came when World No.1 Koepka, who held an early one-shot lead, lost a ball from an errant tee shot at the 7th hole and made double bogey.

Koepka's final-group playing partner McIlroy made a timely birdie on the same hole to steal the lead in a three-shot swing and he never looked back.

Victorian Marc Leishman shot a 67 to finish tied for 24th at two over to take home US$450,500 (AU$670,800).

- Evin Priest, Australian Associated Press