KIAWAH ISLAND, S.C. (AP) — Phil Mickelson has delivered so many thrills and spills over 30 years of pure theater that no one ever knows what he will do next.

His latest act was a real stunner: A major champion at age 50.

Mickelson captured his sixth major and by far the most surprising Sunday at the PGA Championship. He made two early birdies with that magical wedge game and let a cast of contenders fall too far behind to catch him in the shifting wind of Kiawah Island.

He closed with a 1-over 73, building a five-shot lead on the back nine and not making any critical mistakes that kept him from his place in history.

Julius Boros for 53 years held the distinction of golf’s oldest major champion. He was 48 when he won the 1968 PGA Championship in San Antonio.

Pure chaos broke out along the 18th hole after Mickelson hit 9-iron safely to just outside 15 feet that all but secured a most improbable victory. Thousands of fans engulfed him down the fairway — a scene typically seen only at the British Open — until Mickelson emerged into view with a thumbs-up.

Chants of “Lefty! Lefty! Lefty!” chased him onto the green and into the scoring tent, his final duty of a week he won’t soon forget.

Three months after 43-year-old Tom Brady won a seventh Super Bowl, Mickelson added to this year of ageless wonders. Mickelson became the first player in PGA Tour history to win tournaments 30 years apart. The first of his 45 titles was in 1991 when he was still a junior at Arizona State.

Mickelson became the 10th player to win majors in three decades, an elite list that starts with Harry Vardon and was most recently achieved by Tiger Woods.

“He’s been on tour as long as I’ve been alive,” Jon Rahm said. “For him to keep that willingness to play and compete and practice, it’s truly admirable.”

Brooks Koepka and Louis Oosthuizen had their chances, but only briefly. Koepka was 4 over on the par 5s when the game was still on and closed with a 74. Oosthuizen hit into the water as he was trying to make a final run and shot 73.

Mickelson finished at 6-under 282.

The victory came one week after Mickelson accepted a special exemption into the U.S. Open because at No. 115 in the world and winless the last two years, he no longer was exempt from qualifying. He had not finished in the top 20 in his last 17 tournaments over nearly nine months. He worried that he was no longer able to keep his focus over 18 holes.

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And then he beat the strongest field of the year — 99 of the top 100 players — and made it look easy.

The PGA Championship had the largest and loudest crowd since the return from the COVID-19 pandemic — the PGA of America said it limited tickets to 10,000, and it seemed like twice that many — and it clear what they wanted to see.

The opening hour made it seem as though the final day could belong to anyone. The wind finished its switch to the opposite direction from the opening rounds, and while there was low scoring early, Mickelson and Koepka traded brilliance and blunder.

Koepka flew the green with a wedge on the par-5 second hole, could only chip it about 6 feet to get out of an impossible lie and made double bogey, a three-shot swing when Mickelson hit a deft pitch from thick grass behind the green.

Mickelson holed a sand shot from short of the green on the par-5 third, only for Koepka to tie for the lead with a two-shot swing on the sixth hole when he made birdie and Lefty missed the green well to the right.

Kevin Streelman briefly had a share of the lead. Louis Oosthuizen was lurking, even though it took him seven holes to make a birdie.

And then the potential for any drama was sucked out to sea.

Oosthuizen, coming off a birdie to get within three, had to lay up out of the thick grass on the 13th and then sent his third shot right of the flag and into the water, making triple bogey.

Just like that, Mickelson was up by five and headed toward the inward holes, the wind at his back on the way home with what seemed like the entire state of South Carolina at his side.