Justin Thomas overturned a record-equalling seven-shot deficit before beating Will Zalatoris in a play-off to win his second PGA Championship following a dramatic climax at Southern Hills.

Chile's Mito Pereira held a one-shot lead on the 72nd hole after watching his birdie putt on the 17th stop agonisingly short of the hole, but pushed his drive into the creek and ran up a devastating double bogey.

“I wasn't even thinking about the water. I just wanted to put it in play, and I guess I aimed too far right. I just hit in the water,” Pereira said.

“I was feeling the same. I wasn't like really different. It was like that all day. I mean, I thought I was nervous the first day. Then I thought I was nervous the second day. Then I thought I was nervous on the third day but the fourth day was terrible. I mean, this morning was tough.”

RIGHT: Thomas celebrates with caddie Jim 'Bones' Mackay. PHOTO: Andrew Redington/Getty Images.

That left Thomas and Zalatoris to contest a three-hole aggregate play-off and Thomas birdied the 13th and 17th and parred the 18th to lift the Wanamaker Trophy for the second time, having started the day seven shots off the lead.

That meant the former World No.1 equalled the biggest comeback in PGA history, John Mahaffey coming from seven behind Tom Watson after 54 holes to defeat Watson and Jerry Pate in a play-off at Oakmont in 1978.

"I was asked early in the week what lead is safe and I said, 'No lead,'" Thomas said. "I can't believe I found myself in a play-off.

Thomas had holed from six feet on the par-5 13th to match the birdie Zalatoris had made after finding the green in two, but Zalatoris missed from eight feet for birdie on the 17th after Thomas had driven the green on the 302-yard par-4 to set up a two-putt birdie.

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Zalatoris then could not hole his lengthy birdie putt on the 18th and Thomas safely two-putted for par to get his hands on the Wanamaker Trophy for the second time following his 2017 win at Quail Hollow.

Thomas had birdied the 17th in regulation and missed from 10 feet for another on the last, his third 67 of the week setting a target of five-under-par that only Zalatoris was able to match.

Pereira reacts during the closing stages of Sunday's final round. PHOTO: Christian Petersen/Getty Images.

Pereira and Cameron Young shared third at four-under and England's Matt Fitzpatrick and Tommy Fleetwood tied for fifth a further stroke back.

Rory McIlroy's second successive Sunday charge in a major had earlier ended in disappointment, with the former World No.1's closing 68 only good enough for outright eighth at two-under as his wait for a fifth major title, and first since the 2014 PGA, goes on.

McIlroy finished runner-up in the Masters thanks to a closing 64 at Augusta National, a round which culminated in wild celebrations from the four-time major winner after he holed a bunker shot on the 72nd hole.

In stark contrast, McIlroy declined to speak to waiting reporters on Sunday before quickly collecting his belongings from the locker room and heading to his car.

The reaction was understandable given that McIlroy had enjoyed a one-shot lead following an opening 65 from what proved the favourable side of the draw.

Cameron Smith (69) and Lucas Herbert (71) finished as the leading Australians in a tie for 13th at even par for the championship.