A third round of 70 left Koepka on 12 under par and seven shots ahead of world number one Dustin Johnson, Harold Varner, Luke List and Thailand’s Jazz Janewattananond, with England’s Matt Wallace and Japan’s Hideki Matsuyama a shot further back.
Greg Norman famously lost a six-shot lead in the final round of the 1996 Masters, but asked if he had any doubts about completing a wire-to-wire victory on Sunday, Koepka said: “No. I feel confident. I feel good. I feel excited.
“I don’t know what the (weather) forecast is but if I can hit a few fairways, there’s really a couple of key holes out here. If you play seven well, play 10 and 12 well, then from there you just hit the centre of the greens and try to par this place to death.
“I’m definitely not going to let up, I promise you that. I’d love to force it on the field and make it where it’s as big as a lead as I possibly can get. It would be nice to be able to make a 10 on the last hole and be okay.
“But I’m just playing to play good golf and wherever that puts me, I’ll be satisfied if I just go play one more good round.
“If you start treating tomorrow’s round differently than every other round, I feel like that’s where I would maybe be nervous.
“It’s just like any other round I’ve ever played. It’s 18 holes. Try to hit the fairway. Try to hit the green and try to make birdie.”
Defending champion Brooks Koepka continued to tear up the record books as he took a stranglehold on the US PGA Championship and made a mockery of Bethpage’s fearsome reputation.
Koepka followed his course record of 63 on Thursday with a second round of 65 for a halfway total of 128, two shots better than the previous lowest in major history shared by Nick Faldo, Brandt Snedeker, Martin Kaymer, Jordan Spieth and Gary Woodland.
At 12 under par the 29-year-old enjoyed a seven-shot lead over Spieth and Adam Scott, surpassing the previous biggest 36-hole lead in tournament history of five shots set by Nick Price in 1994.
Koepka also finished a staggering 17 shots ahead of playing partner and Masters champion Tiger Woods, who missed the cut after adding a 73 to his opening 72.
Woods had been the only player to finish under par when he won the 2002 US Open at Bethpage, with Lucas Glover winning on four under when the tournament returned to the same venue seven years later.
Koepka, who is seeking a fourth major victory in his last eight starts, said: “Today was a battle. I did not hit it very well today, I was fighting a bit of a block. I was able to find a couple of fairways and when I did miss I was in a great lie. I’m still putting really well which is big.
Stone cold Brooks Koepka is looking for another Wanamaker. pic.twitter.com/RMuURrT6oE— PGA Championship (@PGAChampionship) 17 May 2019
“I feel good, especially the way I battled today, to not have it and get that score I am very proud of myself. I fought hard, I feel great and just need to continue on the weekend.”
Scott had the chance to equal or even better Branden Grace’s all-time major record of 62 – set in the 2017 Open at Royal Birkdale – when he played the first 14 holes in seven under par, only to miss from two feet for par on the 17th and have to settle for a 64.
Spieth had earlier breathed new life into his bid to become the sixth player to complete a career grand slam thanks to a 66, the 25-year-old having started the week by admitting he was “in a bit of a slump” after failing to record a top-20 finish all season.
Asked if the prospect of joining golf’s most elusive club had crept into his mind, Spieth said: “It certainly hasn’t. I can’t imagine it will because I haven’t been in contention on a Sunday since the Masters last year.
“If I’m able to put some good work in tomorrow, then I will be in contention on Sunday and at that point, it will be just more (thinking) of trying to win a golf tournament. It won’t matter to me what tournament it is.”
England’s Matt Wallace shares fourth place with world number one Dustin Johnson, Daniel Berger and Kelly Kraft, although the quartet are eight shots off the pace, with Justin Rose another stroke back and Tommy Fleetwood on two under.
Rory McIlroy looked set to miss the cut when he limped to the turn in 40 after dropping five shots in his first three holes, but the four-time major winner produced a hat-trick of birdies from the fourth and picked up another shot on the eighth.
“I just needed to see one putt to go in, to see something hit the bottom of the hole and that was on the fourth,” McIlroy said after making the weekend with nothing to spare. “From there I started to play some good golf.
“I had a horrendous start, five over after three, but came back well and the goal after those three holes was to be here for the weekend and it looks like I have done that, which is nice.”
Woods led at Carnoustie with eight holes to play before finishing sixth behind playing partner Molinari, who held his nerve to card a bogey-free 69 to become the first Italian player to win a major title.
The 36-year-old Ryder Cup star takes a two-shot lead over Woods and Tony Finau into Sunday’s final round at Augusta, with the tee times brought forward in an effort to avoid thunderstorms forecast to hit the course in late afternoon.
“I think, to be honest, every tournament is different and every time is a different story,” Molinari said after a superb third round of 66. “He (Woods) obviously loves this place and he’s playing great golf.
“So I’m aware that it’s not going to be easy and I can just do my best. But it’s not like I can only worry about him. There’s a lot of guys I think in with a chance.
“We’ve seen in the past years that a few shots’ lead really doesn’t mean too much and we’ve seen today that you can shoot seven, eight under the way the course is playing. I think there’s a lot more guys with a chance.
“Coming from Italy, it’s exciting just to walk down Magnolia Lane. I don’t have to be in the last group on Sunday to be excited. It’s a special week. It’s always been a special week for me, even in the last few years where I didn’t play so well.
“I’ll just try to enjoy tomorrow as much as possible, and again, do my best, shot by shot, don’t get ahead of myself and see what happens.”