Koepka bullied rain-softened Bellerive on Saturday on the front nine and built a four-shot lead, only to run into bad patch that brought a strong list of contenders into the mix - including Tiger Woods - going into the final round of the PGA Championship.
Despite the record showing, he leads Kevin Kisner (9-under-par) by just one stroke.
Only a three-putt bogey at the fifth hole halted his progress, though he put the setback quickly behind him to birdie the next three holes.
Finau completed his adventurous second round Saturday morning, finishing with 10 birdies in a 4-under-par 66 that was good enough to make the cut.
"A kid legit just passed out right before Tiger teed off on No. 12", Kyle Porter tweeted.More news: Look to the Skies This Weekend for a Colorado Meteor Shower
The four-time PGA Championship victor Woods ignited hopes among enormous galleries at the St. Louis course when he picked up four shots on his front nine. Woods slid his lag putt by the hole, then missed a short comeback putt for par.
Meanwhile, Koepka will take a two-shot lead over Australian Adam Scott into the final round on Monday after shooting a four-under 66 that left him at 12-under for the tournament.
A former world number one and the 2013 Masters victor, Scott muscled his way into second place on 10-under, while Spaniard Jon Rahm (66) and Americans Rickie Fowler (69) and Gary Woodland (71) were three behind.
Woodland's 36-hole score broke the PGA record by one shot, most recently set by Jimmy Walker and Robert Streb at Baltusrol.
Defending champion Justin Thomas also made birdie, his third in the last four holes, to close within four of the lead on six under.More news: Frank Lampard reveals why Leeds United beat Derby in Championship demolition job
Woods birdied five of his first eight holes and made the turn in four-under 31 before making nine pars on the back side, the most disappointing of which came at the par-5 17th.
Koepka, who in June became the first man to win back-to-back US Opens since Curtis Strange in 1988-89, could become only the fourth player to win the US Open and PGA Championship in the same year, following fellow Americans Gene Sarazen in 1922, Ben Hogan in 1948 and Jack Nicklaus in 1980. "Having said that, I would have shot a much higher score yesterday". You get away with more. "But you just feel like you can have lots of chances".
'I actually played well on the back nine in both rounds, ' insisted Woods, with good reason.
"Obviously things haven't been going well for me this year". "I shouldn't have been that aggressive with that first putt and it cost me".
He won't get to No. 1 in the world with a victory on Sunday, but he'll certainly make a statement that will be impossible for anyone to ignore.More news: Australian woman killed by garbage truck in New York City
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