TULSA, Okla. — All day, Justin Thomas was lying in wait.

All day, Mito Pereira was leading.

Thomas began the day seven shots out of the lead. He was an afterthought. He figured to go as low as he could go and see what happened.

The 104th PGA Championship was Pereira’s to lose.

And lose it Pereira did … until Thomas went and won it.

In a stunning turn of events, the 27-year-old Chilean playing in only his second career major championship and who took a three-shot 54-hole lead into Sunday’s final round, had at least a piece of that lead all day … until he finished the 18th and final hole, the 72nd of the tournament.

Pereira, standing on the 18th tee with a one-shot lead over Justin Thomas and Will Zalatoris, pushed his tee shot into the creek that runs down the right side of the 18th fairway and took double bogey.

Suddenly, he was done, out of the tournament and Thomas and Zalatoris were heading to the 13th tee for a three-hole aggregate playoff — Nos. 13, 17 and 18.

It all happened so fast.

So, too, did the playoff, which Thomas won thanks to birdies on the first two holes of extra time, on 13 and 17, to capture his second career major championship.

“It’s funny, I was asked earlier in the week about what lead is safe and I said, ‘No lead is safe,’ ’’ Thomas said afterward. “This place is so tough. I stayed so patient … I just couldn’t believe I found myself in a playoff. I wasn’t looking at leaderboards today. I was just trying to play golf.’’

He shot 67, the lowest round anyone posted on Sunday.

When it was over, after Thomas two-putted for par on 18 and clinched victory, he looked stunned as he hugged his caddie, Jim “Bones’’ Mackay, and clenched his eyes shut. He shook Zalatoris’ hand and shook his head, looking to the sky and exhaling.

Then came his parents onto the green for hugs, and then his fiancée as the massive crowds enveloping the 18th green sitting below the clubhouse with the skyline of Tulsa in the background chanted, “JT, JT, JT.’’

“It hasn’t sunk in just yet,’’ Thomas said. “I was jittery and I almost kind of couldn’t feel my limbs walking up to that tap-in on 18.’’

What a day. What a beautifully bizarre day that broke out.

And what a shame for Pereira. You never wish anyone to lose the way he did.

Crazy things have happened on that Southern Hills 18th hole. Ask Stewart Cink. In the 2001 U.S. Open, Cink missed an 18-inch putt on the 72nd hole that would have gotten him into an 18-hole Monday playoff that Retief Goosen would eventually win over Mark Brooks.

“On 18, I wasn’t even thinking about the water,’’ Pereira said. “I just wanted to put it in play, and I guess I aimed too far right. I just hit in the water. Obviously sad to be here and not in the playoff, not make par, just straight win.’’

Pereira conceded to being “nervous’’ not only on Sunday, but every day this week.

“I thought I was nervous the first day, then I thought I was nervous the second day, then I thought I was nervous on the third day, but the fourth day was terrible,’’ he said. “I mean, this morning was tough. I just played it through, and actually had a one-shot lead on 18 and that was pretty good and sad to hit it in the water.’’

He said he thought he hit that tee shot “low and straight,’’ adding, “I’m really confident with that one. I don’t know what happened. I mean, I wish I could do it again.’’

There, of course, are no do-overs in golf. Ask Greg Norman. Ask Jean Van de Velde. Ask the long list of players who’ve thrown away major championships after they appeared to have them in hand.

“It’s not how I wanted to end up this week, but really good result,’’ Pereira said.

Zalatoris, a marvelously talented player who has it all, walked away still seeking his first PGA Tour victory, though he’s had uncanny success in major championships already, having finished runner-up at the 2021 Masters.

“I can do it,’’ he said. “Obviously, I’m pretty close. I didn’t have my best stuff [Saturday], which ultimately was kind of the difference. I battled like crazy today. I’m close and I’m super motivated, but we’ll get one soon.’’

Thomas, meanwhile, has been poised to add another major to the 2017 PGA he won at Quail Hollow.

“It was a bizarre day,’’ he said. “I definitely crossed one off the list. Bones did an unbelievable job of just keeping me in the moment today.’’

What a moment it was.