KIAWAH ISLAND, S.C. -- Phil Mickelson captured his sixth major and by far the most surprising on Sunday at the PGA Championship, becoming, at the age of 50, the oldest winner in the 161 years of major championship golf.
Mickelson never thought he was too old to win again, much less a major. He just didn't have much evidence on his side until a remarkable four days at Kiawah Island, where he kept his nerve and delivered all the right shots for his first major win since 2013.
He made two early birdies with that magical wedge game that never left him and then let a cast of challengers fall too far behind to catch him in the shifting wind off the Atlantic.
"One of the moments I'll cherish my entire life,'' Mickelson said. "I don't know how to describe the feeling of excitement and fulfillment and accomplishment to do something of this magnitude when very few people thought that I could.''
That list of people didn't include Mickelson. Never mind that he had not won in more than two years, had not registered a top 20 in nearly nine months and last won a major in 2013 at The Open. Never mind that he was No. 115 in the world.
"This is just an incredible feeling because I believed it was possible, but everything was saying it wasn't," Mickelson said.
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.
The record now belongs to Mickelson, whose legacy is as much rooted in longevity as any of the skills that have made him among the most exciting players in the game.
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.
Woods, who won the Masters in 2019 at age 43 after four back surgeries, was among those to send a tweet of congratulations.
Truly inspirational to see @PhilMickelson do it again at 50 years of age. Congrats!!!!!!!— Tiger Woods (@TigerWoods) May 23, 2021
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.
"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.''
Koepka and Oosthuizen had their chances, but only briefly. Koepka was 4 over on the three par-5s he faced 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.
"Phil played great,'' Koepka said. "It's pretty cool to see, but a bit disappointed in myself.''
This was history in the making, and no one wanted to miss it.
Pure chaos broke out along the 18th hole after Mickelson hit 9-iron safely to just outside 15 feet and all but secured a most improbable victory. Thousands of fans engulfed him down the fairway -- a scene typically seen only at the Open Championship -- until Mickelson emerged into view with a thumbs-up.
"I've never had an experience like that," Mickelson said. "Slightly unnerving but exceptionally awesome.''
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.
Tom Watson came close at Turnberry in 2009 when, at age 59, he had a 1-shot lead playing the 18th hole and made bogey, losing The Open in a playoff to Stewart Cink. Greg Norman was 53 when he had the 54-hole lead at Royal Birkdale and failed to hang on in the 2008 Open.
Mickelson didn't let this chance pass him by.
"It was like the Phil that I remember watching just when I turned pro, and it was great to see,'' Oosthuizen said. "I mean, what an achievement to win a major at 50 years old, and he deserves all of that today.''
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 past two years, he no longer was exempt from qualifying. As recently as a month ago, he was concerned that he could not keep his focus for 18 holes and kept throwing away shots that set him back.
And then he beat the strongest field of the year -- 99 of the top 100 players -- and made it look easy at times.
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 was clear what the fans 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 3-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 2-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. 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 3, 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 5 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.
The next stop is the U.S. Open at Torrey Pines, the only major keeping Mickelson from the career Grand Slam.
"It's very possible that this is the last tournament I ever win, like if I'm being realistic,'' Mickelson said. "But it's also very possible that I may have had a little bit of a breakthrough in some of my focus and maybe I go on a little bit of a run. I don't know.
"But the point is that there's no reason why I or anybody else can't do it at a later age. It just takes a little bit more work.''
Even at 50, Mickelson still keeps everyone guessing what he will do next.
The Associated Press contributed to this report.