The 29-year-old, who won this tournament for his first back in 2022, started the day seven shots back of the lead, but posted the clubhouse lead at five-under with his third round of 67 of the week. He was joined in the three-hole play-off at Southern Hills by Zalatoris, who now has five top-ten finishes in the eight majors he has competed in.
It was Zalatoris who looked to have the advantage on the first hole of the play-off, the par-five 13th, as he found the green in two and Thomas was forced to layup.
But a wonderful flicked wedge shot followed from Thomas as he made birdie, which Zalatoris could only match as his eagle putt rolled just past the left edge.
Onto the driveable par-four 17th. The eruption from the grandstands around the green told the story as Thomas stepped up first and found the green with a stunning drive, before Zalatoris sent his response right of the greenside bunkers.
A chip to seven feet gave Zalatoris the chance to make birdie, a chance he couldn’t take as Thomas then two-putted to take a one-shot advantage to the 18th.
Another perfect drive put Thomas in the ideal position on the fairway and a stress-free par did the job, giving him his first major title with Jim ‘Bones’ Mackay, Phil Mickleson’s former caddie, on his bag.
Mito Pereira, the 27-year-old in just his second major appearance, took a three-shot lead into the final round and still had one of those standing on the 72nd hole.
With Thomas and Zalatoris in the clubhouse on five-under, par would have been good enough for the Chilean. But his drive found the water and in a cruel finish he was unable to even make a par - a double-bogey six meant he missed out on the play-off.
Tommy Fleetwood posted an impressive final round 67, playing his last seven holes in five-under, to secure a tie for fifth and the Englishman looks to be nearing his best form once again.
He finished alongside Matt Fitzpatrick, who was never able to get it going in the final group in what was his first real experience of contending for a major. The Sheffield man will be relishing the US Open next month though at Brookline, a course he won the US Amateur title in 2013.
There was a typical Sunday charge from Rory McIlroy who faltered on Friday and Saturday, having put his opening-round woes behind him to lead after 18 holes. He birdied four of his first five holes in the final round to threaten something special, but no more followed and he finished in eighth on two-under-par.
Tiger Woods was unable to tee it up on the final day in Oklahoma, withdrawing after the third round as he shot 79 and visibly struggled with a leg injury he continues to try and recover from.