TULSA, Okla. — Justin Thomas didn’t pay attention to any score but his own on Sunday in the PGA Championship, knowing he was 7 shots behind but with only six players ahead of him on a Southern Hills course where anything could happen.

He never could have dreamed how it all played out, a chaotic final hour of pressure moments, clutch putts and unimaginable heartache for Mito Pereira.

Thomas hit a shank on the sixth hole. He made a 65-foot birdie putt that began his record-tying comeback. He missed a 10-foot birdie putt on the final hole that he feared would cost him. He never led until one hole remained in his three-hole aggregate playoff with Will Zalatoris.

And when Thomas tapped in for par to capture another PGA Championship title, he stood erect on the 18th green with a mixture of joy and disbelief.

“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 playoff.”

Thomas closed with a 3-under 67 that turned out to be enough for a playoff when Pereira, the 27-year-old from Chile in his first PGA Championship who had never trailed all day, drove into a creek and made double bogey on the 18th hole to finish 1 shot behind.

There had not been a playoff in a major since the 2017 Masters, when Sergio Garcia beat Justin Rose. The 19 straight majors without a playoff was the longest streak in major championship history.

Just like his first PGA title at Quail Hollow in 2017, the signature shot for Thomas came on the 17th hole. It was the second hole of the aggregate playoff. He drilled a 3-wood on the 301-yard par 4 to 35 feet for a two-putt birdie, his first lead of the day.

Zalatoris, whose must-make 8-footers for birdie and par on the final two holes of regulation got him into the playoff with a 71, couldn’t deliver in overtime. His 8-foot birdie putt on the 17th in the playoff missed, and he couldn’t catch Thomas at the end.

Zalatoris looked like he had thrown away his chances for a first major win — and a first PGA Tour victory — when he three-putted from just outside 20 feet on the 16th hole. But he responded with a birdie from the bunker at the 17th and holed an 8-foot par putt on the 18th for a 71.

He joined Thomas at 5-under 275, and they played on when Pereira faltered.

Thomas, who had gone 14 months since his last victory at the Players Championship last year, now has a PGA Tour win in each of his past eight years and moves to No. 5 in the world. Since winning his first PGA Tour title during the 2015-16 season, Thomas’ 15 victories are tied with Dustin Johnson for the most of any player.

His second major came when he least expected it.

None of the six players ahead of him had ever won a major. Thomas knew that. He was in the longest drought since his first PGA Tour title. He was aware of that too.

“I remember how tough it is now to win, so I knew I was going to be nervous, and I knew they’d be feeling the exact same thing,” Thomas said. “You just don’t know what’s going to happen.”

John Mahaffey in the 1978 PGA Championship at Oakmont was the other player to come from 7 shots behind on the final day. He also won in a playoff, over Tom Watson and Jerry Pate.

Thomas was still 7 shots behind when he made his remarkable run, a mixture of key birdies and keeping mistakes off his card. It started with an improbable birdie putt from just short of the green to a back pin on the par-3 11th. He edged closer with an 18-foot birdie on the next hole.

He was lurking, while the leading pack behind him was leaking oil.

Zalatoris and Cameron Young each caught Pereira, ever so briefly. All of them found trouble in the rough, sand and greens.

Playing with Zalatoris, a former roommate at Wake Forest, Young, whose father is a longtime PGA professional, was in the mix all day and was briefly tied for the lead. His hopes ended on the 16th when he found a bunker right of the green, blasted out weakly to 30 feet and three-putted for a double bogey. He closed with a 71.

Rory McIlroy made a brief run with four straight birdies on the front nine, putting him at 4-under par for the tournament. He was 2 over the rest of the way and finished eighth.

In eight majors at Southern Hills, it was the first time a player rallied from any margin to win, and it was only the second playoff. Retief Goosen won the other in the 2001 U.S. Open after he three-putted from 12 feet on the final hole.

Thomas closed at 14-1 to win the PGA Championship at Caesars Sportsbook. His odds were as long as 28-1 entering Sunday’s final round.

Out of the 22 players to win multiple PGA Championships, Thomas, 29, is just the fifth to win the event twice before turning 30 years old.

The Associated Press contributed to this report.