Justin Thomas capped a breathtaking comeback by beating Will Zalatoris in a three-hole playoff to win the PGA Championship on Sunday after Chile's Mito Pereira blew a one-shot lead on the final hole.

The playoff ended a day of pulsating drama at Southern Hills Country Club that saw Thomas stage one of the greatest comebacks ever in a major and Pereira suffer one of the most calamitous collapses.

Seven strokes back at the start of the final round, Thomas seized his chance in the playoff to clinch the Wanamaker trophy with a tap-in par on the 18th to beat Zalatoris by one.

It was a second major victory for Thomas, who also won the PGA Championship in 2017.

"I had a good feeling," said Thomas. "Although I was so far back there wasn't that many guys ahead of me, and it's a very tough golf course and anything could happen."

Thomas's rally from seven shots back was the largest final round comeback at the PGA Championship and it certainly impressed his good friend Tiger Woods, who also knows something about comebacks.

The 15-time major winner, who withdrew from the tournament on Saturday after carding a nine-over 79, offered "Big congrats" to Thomas on Twitter.

"He kept himself in this championship until the very end and once he got his shot he didn’t look back," said Woods, who was playing his second event after a car crash 15 months ago nearly cost him his right leg.