The three-time major winner has been much more dominant than Tiger Woods was when he took home the 2002 U.S. Open title at the course in Farmingdale, New York. In 2002, Woods led after all four rounds and won by three strokes as the only player under par for the tournament.
Koepka, who sits at 12 under, is not expected to face much competition from others in the field.
Four golfers are tied for second place at five under, but they would need a record-setting day and a monumental collapse from the leader to even have a chance of winning the Wanamaker Trophy.
The final round got underway at 7:35 a.m. ET, but the leaderboard should not change much until the final groups hit the course in the afternoon.
Brooks Koepka (-12)
Harold Varner III (-5)
Jazz Janewattananond (-5)
Luke List (-5)
Dustin Johnson (-5)
Hideki Matsuyama (-4)
Matt Wallace (-4)
Xander Schauffele (-3)
Jordan Spieth (-3)
Adam Scott (-3)
Patrick Cantlay (-3)
Full leaderboard and live updates can be found here on PGA.com.
Storylines to Watch
How Dominant Will Koepka Be?
Koepka's first-round 63 and second-round 65 put him in a great place on top of the leaderboard.
Even though Koepka looked mortal with a third-round 70, no one was able to catch up to the three-time major winner because of the lead he built up.
Koepka's dominant play has had an affect on the mentality of the rest of the field, as Xander Schauffele pointed out to GolfChannel.com's Will Gray.
"I don't know if the tournament is less fun because I'm 15 shots back or whatever it is," Schauffele said. "But it's very melancholic after today, I'd say, just because every time I look up, I'm 10 or 12 back. So no one likes to play for second, but that's sort of what he's doing to us."
Although Koepka has already been crowned as the champion by many, he still has to play 18 holes to lock up his fourth major crown since 2017.
In order to do that, Koepka needs to once again get off to a strong start on the front nine. On Thursday and Friday, Koepka carded three birdies in the first five holes, while he recorded two birdies in that same stretch Saturday.
If Koepka displays the same control of the opening five holes Sunday, he should be able to extend his lead and demoralize his contenders even more than he already has.
If he completes his 72-hole dominance of Bethpage Black, Koepka will hold back-to-back titles at two different majors, which is something Jack Nicklaus and Tiger Woods never achieved.
Can Unknown Players Finish Off Incredible Tournaments in Top 10?
If Koepka was not so far out in front of the field, we would be hearing more about the collection of relative unknowns playing well behind him.
Harold Varner III, Jazz Janewattananond, Luke List, Matt Wallace and Patrick Cantlay all landed in the top 10 after the third round.
All of the players mentioned above are looking for their best major finish ever, which is an accomplishment that deserves some praise during Sunday's broadcast.
In order to finish off their incredible tournaments, the unfamiliar names at the top of the leaderboard have to play well and hold off surges from Dustin Johnson, Adam Scott, Jordan Spieth and others.
Not only would a high finish land those golfers a large payout, it would secure them in the field for the 2020 PGA Championship, as the top 15 players from the previous year's tournament directly qualify.
Cantlay and Wallace are the likeliest players of the group to remain near the top by the time Sunday ends.
Wallace, who is the 31st-ranked golfer in the world, has missed the cut in four of the last six majors, and the only other time he made the cut was when he tied for 19th a year ago at the PGA Championship.
There is also a possibility that a player from one of the early tee times takes advantage of the course to surge into the top 15 while setting the tone for the day's scoring.
Of the players currently over par, eight of them carded under-par rounds Saturday, including Americans Sam Burns and Adam Long.
Follow Joe on Twitter, @JTansey90.