RORY McIlroy has become $15 million richer after a nail-biting four-hole sudden death victory over Ryan Moore at the season-ending Tour Championship in Atlanta, Georgia.

The Northern Irishman captured the FedEx Cup bonus prize of $AU 13 million on the fourth extra hole with a clutch birdie butt to trump a stellar up-and-down par from American Moore, in addition to banking the $1.5 million paycheque ($AU2 million) for winning the US PGA Tour season’s final event.

Kevin Chappell was eliminated after the first playoff hole – East Lake’s par-5 18th – and from there the two remaining golfers battled down 18th once more, before playing the par-3 15th and finally the par-4 16th.

All three players found themselves tied at 12-under par after regulation play, with Moore and McIlroy shooting final round 6-under 64s and Chappell carding a 4-under 66.

McIlroy looked to have the sudden death playoff in the bag on the first extra hole when he nailed a 357-yard drive and put his second shot to within 10 feet. But the putt lipped out and he and Moore, also with a birdie, went back to the 18th tee.

FedEx Cup points leader Dustin Johnson fired a disappointing 3-over 73 to almost rule himself out of winning the lucrative bonus prize, but still would have claimed the $13 million prize if Chappell or Moore won the Tour Championship.

The only Australian near the leaderboard was Adam Scott – who finished at 4-under and eight shots back – after Jason Day withdrew mid-round on Saturday with the same back injury that rubbed him out of the BMW Championship mid-tournament.

“It was incredible; all I wanted to do is win the Tour Championship,” McIlroy said after winning golf’s richest prize. “I couldn’t control what anyone else was doing … big credit is due to Ryan (Moore); he’s playing fantastic golf and has done over the past few months.

“I played really well last week (at the BMW Championship) and I feel like my game’s coming together at a really good time.”