Thomas needed plenty of help, and Mito Pereira provided it in a tragic finish. The 27-year-old from Chile, playing in only his second major, took a one-shot lead to the final hole and drove into a creek to make double bogey.
It was the first time since Phil Mickelson at Winged Foot in the 2006 U.S. Open that a player lost a one-shot lead in the final hole to lose a major.
Zalatoris looked like he had thrown away his chances for a first major – and 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 victory in each of his last eight years and moves to No. 5 in the world.
John Mahaffey in the 1978 PGA Championship at Oakmont was the other player to come from seven shots behind on the final day. He also won in a playoff over Tom Watson and Jerry Pate.
Thomas was still seven shots behind when he made his remarkable run, a mixture of key birdies and keeping mistakes off his card. It started with a 65-foot 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 and in the sand. Thomas nearly holed a long bunker shot on the 16th, made birdie from a left bunker on the reachable 17th and had a 10-foot birdie putt he thought he needed at the end.
He missed and got a reprieve.
Pereira was on the cusp of becoming Chile’s first major champion and giving South America the career Grand Slam.
Even after five bogeys, he never lost the lead and delivered clutch par saves from the bunker left of the ninth green and from well behind the 10th green. None was bigger than his 12-foot putt on the 16th to stay one shot ahead.
It all came undone with one swing.
His sawed-off swing with the driver, so effective on the previous hole, peeled to the right and into the creek down the right side of the 18th fairway. After a penalty drop, his approach up the hill started left and never cut back, landing in the rough. His chip rolled off the back edge of the green.
His double bogey gave him a 75, a hard-luck end to such a promising week.
“On Monday, I just wanted to make the cut. On Sunday, I wanted to win,” Pereira said. “I’ll take this to learn for the future.”
Young, whose father is a longtime PGA professional, also will look back at missed chances. Playing with Zalatoris, a former roommate at Wake Forest, Young was in the mix all day and was briefly tied for the lead. His hopes ended on the 16th went 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.