LOS ANGELES (AFP) — A nervy Wyndham Clark birdied the final three holes to dramatically win the BMW Championship on Sunday, having earlier surrendered his five-stroke lead to Rory McIlroy.

Clark had claimed his second US Open title earlier this summer by barely clinging on to a huge final-day advantage, and history repeated itself at the penultimate event of the PGA Tour's FedEx Cup playoffs.

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Having struggled all day, Clark finally made his first birdie on 16, followed it with another on 17, and watched on with relief as his final pair partner McIlroy bogeyed after finding two separate bunkers.

Clark sealed the memorable win with a 17-foot putt for a third straight birdie, and a round of 70 to finish at 17-under par.

"It was weird. I wasn't really nervous. I was kind of like out of it, and I just was making just dumb bogeys," Clark said.

"As much as I would have loved to run away with this, it was fun getting the juices going, and (to) really feel the angst coming down at the end," he added.

Clark's five-shot overnight advantage had immediately dropped to three on the first hole at Bellerive Country Club in St. Louis, Missouri, as he three-putted for bogey while McIlroy opened with a birdie.

Gary Woodland then cut the gap to two, with birdies on two, four and five.

A jittery Clark wobbled as the pressure mounted. He saved par on five after totally mis-hitting a simple fairway approach, then bogeyed the next hole after a heavy chip.

The double Major winner then escaped with par again after hitting the lip of a fairway bunker on eight, before bogeying 10.

McIlroy briefly appeared to falter, with bogeys on four and seven. But he pulled those back with birdies on eight and nine.

And the popular Northern Irishman dramatically tied Clark for the lead with a perfectly judged putt on the 11th green that sent the crowd wild.

The two golfers exchanged pars over the next four holes, before Clark rolled in a 17-foot putt on the tricky par-three 16th for his first birdie of the day.

For the third straight hole, McIlroy narrowly missed his birdie putt, giving Clark a one-shot advantage with two holes to play.

On the par-five 17th, McIlroy from deep rough yanked his ball into a fairway bunker, and found another bunker with his next shot, essentially handing the tournament to Clark, who birdied.

"I don't think I could be too disappointed — I'm probably not playing well enough to be disappointed that I didn't win," McIlroy said.

"But I had my chances on the back nine."

Patrick Cantlay — trying to secure his place in the final field of 30 at next week's Tour Championship — had earlier briefly moved just one back from Clark.

His wild round including five birdies and three bogeys in his first 10 holes, before finding the water on 11 for a double, for his challenge to fade away.

But Cantlay birdied the final three holes to grab second place on 14-under and book a place at the season-ending event in Atlanta, Georgia.

McIlroy finished third on 13-under, followed by the American trio of Chris Gotterup, Collin Morikawa and Gary Woodland a further stroke back.

World No. 1 Scottie Scheffler continued to climb the leaderboard after his nightmare, illness-affected opening day 72.

He finished the tournament seven-under, tied for 12th place.