ST. LOUIS (Reuters) - Brooks Koepka went largely unrecognised when he went to a local fitness centre with Dustin Johnson before Saturday’s third round at the PGA Championship but by day’s end he was on the threshold of golf’s most elite club of young players.

Aug 11, 2018; Saint Louis, MO, USA; Brooks Koepka hits his tee shot on the 3rd hole during the third round of the PGA Championship golf tournament at Bellerive Country Club. Mandatory Credit: Kyle Terada-USA TODAY Sports

The 28-year-old opened a two-stroke lead at Bellerive in the final major of the year, and victory on Sunday would see him equal Jordan Spieth’s haul of three major titles and be one shy of Rory McIlroy’s tally.

Despite defending his U.S. Open title in June, Koepka remains something of an afterthought with the golf public. But he will be very much front of mind for more heralded rivals on course.

“If I do what I’m supposed to, I should win,” he said confidently after carding 66 for a 12-under-par total of 198, two strokes ahead of Australian Adam Scott (65) and three in front of Spain’s Jon Rahm and Americans Rickie Fowler and Gary Woodland.

Tiger Woods, in search of a 15th major title, was four behind on a day when the cream bubbled to the top.

“There’s a lot of star power, and there should be, it’s a major championship,” Koepka added.

“You should see the best players in the world come to the top.”

Koepka was waltzing along with a five-shot lead until his flawless 43-hole stretch ended with a bogey at the par-four 14th.

A second bogey followed on the 15th, where his drive finished behind a tree, prompting him to take a penalty stroke.

“I don’t know how it got behind that tree with so many people on the right-hand side (of the fairway),” he said.

“You would think it would have like hit somebody’s foot and just kind of gone to the side, but to go right in that little wedge of the tree, I don’t know how it did that.

“But you just get on with it. You try to make the best of a bad situation and just keep rolling with it.”

Koepka said his form at last week’s World Golf Championships event, where he finished fifth, had been better than in either of his U.S. Open victories, except for his putting.

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“I like the way I’m hitting the ball, I’m putting much better, and my short game’s on point this week. So when all those add up, I could see why I played so well,” he said.

As for that gym visit with world number one Johnson, Koepka had to laugh at the disparity in the players’ profile.

“Everybody wanted a picture with Dustin,” he said.

“They were talking about him as we left and I was just standing there laughing. They were like, ‘Did you see that number one player in the world was here?’

“I don’t know what to say to that.”