Hovland closed with a two-under 70 on another brutal test on a course baked all week by sun, forcing the play-off with a 30-foot birdie on the 17th – the only one on that hole in the final round – and saving par from behind the 18th green.

The pair ventured back to the 18th for a sudden-death play-off, Hovland barely got onto the front of the green, some 60 feet away from the back pin, and two-putted by holing a seven-footer for par.

It earned the Norwegian a fourth PGA Tour victory and a first on American soil, this one coming with a $US3.6 million ($A5.5m) winner's cheque and a handshake from host Jack Nicklaus.

Hovland's previous wins were in Mexico, twice, and Puerto Rico.

The 25-year-old, who will rise to No.5 in the world rankings, didn't feel as though he did anything special.

His lowest round all week was a third round 69 but he was the only player to break par on all four days.

"I played smart. I played my game," he said.

"And I came up clutch this time."

It was a crushing loss for McCarthy, statistically one of the best putters on the PGA Tour.

The American showed his touch by saving crucial pars and playing bogey-free on a day when the average score was just under 75. His only bogey came on the 18th hole – twice.

"I played smart. I played my game. And I came up clutch this time." – Viktor Hovland.

McCarthy had a one-shot lead when he missed the 18th fairway to the left, pitched out and narrowly missed a 25-foot par putt for the win.

In the play-off, his shot from the right rough rolled back off the green some 50 yards away. He pitched to 12 feet and the putt caught the left edge and spun away.

"I'm heartbroken right now," McCarthy said, emotion in his voice after his closest call to win on the PGA Tour in his 156th attempt.

World No.1 Scottie Scheffler rattled home with a 67 and finished third, missing the play-off by one shot. Remarkable considering, he made the cut on the number.

Scheffler has not finished worse than 12th in his 13 starts this year.

Otherwise, this was a final day when so many went in reverse from the 22 players who had been separated by three shots at the start of the round.

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Third-round co-leader Si Woo Kim closed with a 73 to finish fourth, two shots short of the play-off at five-under, one stroke ahead of Jordan Spieth (71) and fellow American Andrew Putnam (70).

Rory McIlroy chipped in from below the fourth green for birdie and had the lead on the front nine, but he gave away far too many shots on the back – including three bogeys in a row – for a 75 that took him out of the picture.

He eventually shared seventh at three-under with Adam Schenk (71), one better than Adam Scott, who closed with a 71.

The only Australian to make the cut, Scott continues to knock on the door, posting his third top-10 finish from his past four events.