TULSA, Okla. — The dominant story line before the 2022 PGA Championship revolved around Phil Mickelson, who became the oldest major champion last year when he won the event at age 50 but chose not to defend his title. Then the focus of the tournament shifted to Tiger Woods, 46, who arrived at the Southern Hills Country Club to resume his stirring comeback from injuries he sustained in a horrific car crash 15 months ago. But Woods struggled physically, and mired in last place after three rounds, he withdrew before Sunday's final round.

What evolved instead on the last day of the PGA Championship was a glimpse of elite men's golf's youthful future, not its aging past. On a nervy, topsy-turvy afternoon in eastern Oklahoma, there was yet another dramatic showdown between the dazzling, hard-swinging 20-somethings who have overtaken the game.

In a taut, three-hole aggregate playoff after the 18-hole fourth round ended in a tie, Justin Thomas, 29, held off the 25-year-old rising star Will Zalatoris to win his second P.G.A. Championship. The last four winners of golf's major championships, Thomas; Scottie Scheffler, at the Masters; Collin Morikawa, at the British Open; and Jon Rahm, the reigning U.S. Open champion, are in their 20s.

Even in defeat, Zalatoris briefly laughed as he assessed how his generation had become dominant so quickly.

"I kind of have to check myself sometimes because I feel like I'm playing junior golf and college golf all over again," Zalatoris said, mentioning his longtime rivals Scheffler, Thomas and Mito Pereira, 27, who held the lead for most of the fourth round. "We've been playing together for almost 10 years. Now we're at the highest level of golf."

Thomas, who began the final round seven strokes off the lead, did not figure to be celebrating a victory after his first eight holes Sunday when he was one over par. His final-round rally tied for the third-largest comeback in major championship history.

"It was a bizarre day, no doubt," Thomas, who also won the 2017 PGA Championship, said. "But I said in a news conference before the first round that no lead would be safe here — too much wind and too many scary holes."

Pereira, the third-round leader, had appeared poised to become the first golfer from Chile to win a major golf championship. Stepping to the 18th tee Sunday evening, he was playing in the final group and needed only a par to clinch the title.

But Pereira, playing in just his second major championship, sliced his tee shot into a small creek adjacent to the fairway. After a penalty shot drop from the water, Pereira's approach shot found the thick rough alongside the green. His chip from there trundled far across the green until it stopped in the fringe on the opposite side of the green. Pereira made double bogey, and finished in a tie for third place with the American Cameron Young, a college teammate of Zalatoris's when they were at Wake Forest.

"It's such a stressful situation," Pereira said of the atmosphere on the 18th tee. "But I didn't feel any more nervous than other shots today. I wasn't even thinking of the water. But, you know, I wish I could do it again."

The playoff ended a streak of 19 consecutive majors, dating to the 2017 Masters, that did not require extra holes to decide the outcome.

Thomas and Zalatoris began the playoff with birdies on the first hole, the 13th. On the reachable par-4, 302-yard 17th hole, Thomas drove the green and had a lengthy putt for eagle that came up 3 feet short. Zalatoris's drive on the 17th hole was just off the green, and his flop shot stopped 8 feet from the hole. His birdie putt skidded past the hole, and Zalatoris tapped in for par.

With the chance to seize the advantage, Thomas rattled in his birdie putt for a one-stroke edge heading into the third playoff hole, the 18th.

Both golfers reached the 18th green in two shots. Zalatoris could not convert a birdie putt, and Thomas needed only two putts for a par that clinched the championship.

For Zalatoris, it was his latest close call in a major. He finished second at last year's Masters and was tied for sixth at that event last month. He was tied for eighth at the 2021 P.G.A. Championship and tied for sixth at the 2020 U.S. Open.

But on Sunday, Zalatoris, after an even-par front nine, was hampered by poor putting, which has plagued him all season. He bogeyed the 12th and 16th holes but rallied by draining an 8-foot birdie putt on the 17th hole. He also sank a 10-foot putt to save par at the final hole to shoot 71 for the final round and finish at five under par overall. At the time, though, it did not appear to be enough to catch Pereira.

Thomas most likely finished his round with the same feeling. After his rough start to the day, he birdied the ninth hole and had a par at the 10th. Thomas then sank a 64-foot putt from just off the 11th hole for another birdie. At the par-4 12th, he sank an 18-foot birdie putt. Thomas missed consecutive manageable birdie putts at the 13th and 14th holes, but then splashed a shot from a greenside bunker at the par-4 17th hole to within 3 feet, a distance he successfully negotiated for his fifth birdie of the day. That would put him within one stroke of Pereira with one hole to play. A brilliant drive and courageous approach shot to the elevated 18th green stopped 11 feet behind the hole, but Thomas's putt slid past the right edge for a par and a score of 67.

"I was very calm in the playoff and very calm in the final holes before the playoff, which helped a lot," Thomas said. "I was nervous, but it was a different kind of nervous, which maybe comes with experience. It was different than how I felt trying to win my first major in 2017. Whatever it was, it felt right.

"To execute some of those tough shots when you really need to, it was full body chills."