(CNN) The only person who can beat Brooks Koepka heading into the final round of the US PGA is likely to be himself.

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.

Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka successfully defended his PGA Championship title after a thrilling finish at Bethpage Black. Hide Caption 1 of 36 Photos: In pictures: The 2019 PGA Championship so far The 29-year-old clinched his fourth major in eight events after overcoming a late wobble at Bethpage. Hide Caption 2 of 36 Photos: In pictures: The 2019 PGA Championship so far Koepka led by seven ahead of the final day but four straight bogeys on the back nine let in his close friend and the then world No.1 Dustin Johnson, who narrowed the gap to one. Hide Caption 3 of 36 Photos: In pictures: The 2019 PGA Championship so far England's Matt Wallace was in the chasing pack well behind the leading two at Bethpage. Hide Caption 4 of 36 Photos: In pictures: The 2019 PGA Championship so far Popular veteran Phil Mickelson is a fan favorite in New York. Hide Caption 5 of 36 Photos: In pictures: The 2019 PGA Championship so far Koepka said the back nine was "very stressful" as he battled his own mistakes and the pressure exerted by Johnson. Hide Caption 6 of 36 Photos: In pictures: The 2019 PGA Championship so far Japan's Hideki Matsuyama of Japan chips onto the 13th green during the final round of the PGA Championship. Hide Caption 7 of 36 Photos: In pictures: The 2019 PGA Championship so far Tyrrell Hatton of England makes a shot out of the rough amidst the gallery on the ninth hole during the final round. Hide Caption 8 of 36 Photos: In pictures: The 2019 PGA Championship so far Three-time champion Jordan Spieth finished tied third to reignite his major form after a slump of late. Hide Caption 9 of 36 Photos: In pictures: The 2019 PGA Championship so far Johnson faltered coming home and has now finished runner-up in all four of golf's major tournaments. Hide Caption 10 of 36 Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka drives off the 12th tee during the third round. Hide Caption 11 of 36 Photos: In pictures: The 2019 PGA Championship so far Jordan Spieth hits out of a bunker onto the fifth green during the third round of the PGA Championship golf tournament on Saturday, May 18. Hide Caption 12 of 36 Photos: In pictures: The 2019 PGA Championship so far A spectator rests in the shade of a tree along the seventh fairway during the third round. Hide Caption 13 of 36 Photos: In pictures: The 2019 PGA Championship so far Phil Mickelson walks up to the 18th green during the third round. Hide Caption 14 of 36 Photos: In pictures: The 2019 PGA Championship so far Dustin Johnson greets spectators as he walks to the 12th tee. Hide Caption 15 of 36 Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka picks his ball out of the hole after putting on the eighth green. Hide Caption 16 of 36 Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka plays his shot from the 17th tee during the second round of the 2019 PGA Championship on Friday, May 17, in Farmingdale, New York. Koepka, in the lead after the second round, set a record for the lowest 36-hole score in major championship history. Hide Caption 17 of 36 Photos: In pictures: The 2019 PGA Championship so far Tiger Woods tees off on the 18th hole. Woods failed to make the cut for the final two rounds after shooting a three-over 73, ending the tournament at five over. Hide Caption 18 of 36 Photos: In pictures: The 2019 PGA Championship so far Fans cheer for Tiger Woods on the 13th hole. Hide Caption 19 of 36 Photos: In pictures: The 2019 PGA Championship so far Jordan Spieth of the United States lines up a putt on the 16th green during the second round of the US PGA Championship. At the end of the round, Spieth was tied second with Australian Adam Scott. Hide Caption 20 of 36 Photos: In pictures: The 2019 PGA Championship so far Fans line up near the the eighth green during the second round. Hide Caption 21 of 36 Photos: In pictures: The 2019 PGA Championship so far World No.1 Dustin Johnson reacts after putting on the seventh green. Hide Caption 22 of 36 Photos: In pictures: The 2019 PGA Championship so far Phil Mickelson plays a shot from the rough on the third hole. Hide Caption 23 of 36 Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka, left, shakes hands with Tiger Woods after finishing the second round. Hide Caption 24 of 36 Photos: In pictures: The 2019 PGA Championship so far Tommy Fleetwood plays a shot from the fourth tee. Hide Caption 25 of 36 Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka with yet another impeccable drive on the 15th tee in a thrilling opening round of 63 -- a course record. Hide Caption 26 of 36 Photos: In pictures: The 2019 PGA Championship so far April's Masters victory felt a long time ago for Tiger Woods; the 15-time major winner regularly located both rough and bunker in a first round that lacked the control of last month. Hide Caption 27 of 36 Photos: In pictures: The 2019 PGA Championship so far Alex Noren takes stock on the third hole of this thrillingly difficult golf course. If you miss the fairway and the bunkers, the long grass will eat you alive. Hide Caption 28 of 36 Photos: In pictures: The 2019 PGA Championship so far John Daly, the PGA Championship winner in 1991, was making a bit of history at Bethpage Black. He has been given permission to use a golf cart at the tournament as a result of his osteoarthritis in his right knee. Hide Caption 29 of 36 Photos: In pictures: The 2019 PGA Championship so far Phil Mickelson and Jason Day salute their fans as they complete solid first rounds of 1 under par. Hide Caption 30 of 36 Photos: In pictures: The 2019 PGA Championship so far Flowing locks blowing in the wind, Tommy Fleetwood in action en route to a very respectable first-round effort of 3 under par. Hide Caption 31 of 36 Photos: In pictures: The 2019 PGA Championship so far Brooks Koepka putts on a hulking eighth green, watched by fans who were witnessing a clinic from the three-time major winner. Hide Caption 32 of 36 Photos: In pictures: The 2019 PGA Championship so far Jason Day's only major victory came in the 2015 PGA Championship. Here he is, one of many to find one of Bethpage Black's daunting sandpits. Hide Caption 33 of 36 Photos: In pictures: The 2019 PGA Championship so far Dustin Johnson, the world No.1 and a favorite among many experts, tees off at the 17th. Hide Caption 34 of 36 Photos: In pictures: The 2019 PGA Championship so far As Phil Mickelson watches his tee shot fly into the distance, his fans make sure to leave with their own memories. Hide Caption 35 of 36 Photos: In pictures: The 2019 PGA Championship so far An image to highlight the extent of this monster golf course. Narrow fairways, damp, long roughs, gaping bunkers, overhanging trees. But then, Brooks Koepka on the tee, helping himself to the most supreme first round of major golf imaginable. Hide Caption 36 of 36

'Tunnel-vision'

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.

With a 7-shot lead, Brooks Koepka could become the second player to win back-to-back PGA Championship.



The only player to do this is Tiger Woods. pic.twitter.com/xCD88AVAdC — PGA Championship (@PGAChampionship) May 19, 2019

"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.

Comparisons have naturally been drawn with Tiger Woods in his pomp, after beating the Masters champion by 17 shots over two days and forcing the 15-time major winner to admit he's playing a game few can live with, as Woods did in his heyday.

"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."

Brooks Koepka is ploughing a lone furrow at the US PGA.

'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."