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.
Tweet of the day
Eddie Pepperell enjoys a glass of red wine after shooting 11 over par and failing to make a single birdie, usually marked in red on the leaderboard and tweeting "finally some red on the board".
Quote of the day
Brooks Koepka is not satisfied with rewriting the history books, saying "We're going straight to the range. I'm not hitting it that good."
Shot of the day
Koepka was two shots clear when he began his second round but made a statement of intent by smashing a 331-yard drive over the corner of the dogleg before pitching to four feet to set up a birdie.
Round of the day
Adam Scott threatened to equal or even surpass the all-time major record of 62 set by Branden Grace in the 2017 Open when he played the first 14 holes in seven under par before eventually having to settle for a 64.
Statistic of the day
Golf.com columnist Alan Shipnuck points out that with a 17-shot margin between them, Koepka could have given Tiger Woods four shots every nine holes on the first two days and still have come out on top.
A severe pin position on the 221-yard third hole helped it finish as the joint toughest hole of the day with the par-four 15th. Just 10 birdies were made at each hole and a total of 103 bogeys, leaving both playing 0.335 above their respective par.
The par-five fourth played as the easiest hole for the second day running, six eagles and 63 birdies leading to a scoring average of 4.658.
On the up
The chances of a berth becoming available in Oyster Bay when Tiger Woods moves his enormous yacht after missing the halfway cut.
On the slide
The chances of tournament officials receiving a Christmas card from David Lipsky after he was penalised two shots for being late for his tee time.