The all-powerful Koepka leads by seven shots after two record-breaking rounds and a solid third to leave the field trailing in his rearview mirror at Bethpage, New York.
The defending champion shot a level-par 70 on a breezy, sunny Saturday on Long Island to reach 12 under as he tightens his grip on a fourth title in his last eight majors.
The muscular Floridian will play Sunday alongside countryman Harold Varner III, who heads a chasing quartet at five under alongside another American Luke List, Thailand’s Jazz Janewattanond and Koepka’s close friend Dustin Johnson, the world No.1.
The 29-year-old Koepka has been impregnable this week, blending his brute force with a killer short game, deft putting touch and seemingly unflappable, single-minded demeanour.
His opening 63 was a course record and his 65 Friday gave him the lowest 36-hole score in major history. His seven-shot lead heading into the final round is also a US PGA record.
Koepka is aware of the records stacking up, but insists his focus is on just winning a second-straight US PGA to go with back-to-back US Opens.
“I couldn’t care less about breaking any records,” he told Sky Sports. “I’m just trying to win a golf tournament.”
If Koepka’s demeanour is deadpan, his golf has been anything but as his explosive brand of the game has overpowered Bethpage’s infamous Black course this week.
“Everybody keeps asking, like what am I doing differently,” he told reporters. “I’m not — I’m just that much more focused. I think I’m tunnel-visioned.
“It’s just something about playing a tough golf course and understanding. I’m not the best at the birdie-fest. I’m better if it’s going to play very difficult and even par, I like that. Those are my kind of golf courses, where it’s very stressful to play. I enjoy that. That’s what I live for.”
‘I’m going to need some help’
Johnson and co. will be desperately searching for some kind of chink in Koepka’s armor. They may cling to his back-to-back bogeys at nine and 10 Saturday, or a number of drives pushed out to the right, mistakes which could multiply should the pressure of trying to maintain his lead intensify.
Or they may reach for the history books, which record that Scotland’s Paul Lawrie came from a record 10 shots back on the final day to overhaul the befuddled Jean van de Velde in the Open at Carnoustie in 1999.
Then there’s the eight shots retrieved by Jack Burke Jr at the Masters in 1956, or the seven shot deficits erased by Arnold Palmer in the 1960 US Open or John Mahaffey at the US PGA in 1978.
Johnson himself has experience of disappointment at majors and leads disappearing through his hands, such as blowing a three-shot lead heading into the final round of the 2010 US Open at Pebble Beach.
“I’m going to need some help from him [Koepka], and then I’m going to have to play very, very well,” Johnson, the 2016 US Open champion, told reporters.
Koepka, though, isn’t planning to help anyone.
“I know if I can get off to a good start, guys got to push, and if you’re going to push on this golf course, you’re going to make mistakes,” he added.
“I just have to have the same mentality, focus on myself and not anybody else. And at the same time, staying patient and staying in the moment, and every time I do it, I feel like I’m getting better and better at it.”