Gary Woodland maintained his one-shot lead after a morning of record-breaking drama on day two of the US PGA Championship.
The American carded a 66 to get to ten under at Bellerive Country Club, with his 36-hole total of 130 shots the lowest ever in the history of the season's fourth Major Championship.
Countryman Kevin Kisner was then at nine under after a 64, one clear of US Open champion Brooks Koepka, who equalled the lowest round in tournament history with a 63.
South Africa's Charl Schwartzel also carded a 63 to sit at seven under and it was just the second time in Major history that two players had achieved that score on the same day - after Tom Weiskopf and Jack Nicklaus both did it in round two of the 1980 US Open.
Belgian Thomas Pieters and World Number One Dustin Johnson both signed for rounds of 66 to also sit at seven under, a shot clear of South Africa's Brandon Stone who carded a 68.
Playing partners Woodland and Kisner battled it out at the top of the leaderboard all morning before the attention switched to those below them, with Koepka and Schwartzel both having putts to equal Branden Grace's lowest ever Major round of 62.
Kisner started the day three shots off the lead but hit a lovely approach into the first to edge closer to the front and then hit the green in two on the 11th for a birdie-birdie-start.
Woodland also took advantage of the moved-up tee on the par four but Kisner put his tee-shot to four feet on the 13th and when the leader needed three goes to get down from the fringe on the 14th, there was a tie at the top.
A Kisner approach to ten feet on the 15th edged him ahead but Woodland hit a stunning second into the 17th to leave himself five feet for eagle and jump into the lead.
Kisner followed him in for a routine gain, and an approach to 15 feet on the next handed the South Carolina native the lead at the turn.
A nice approach to the second and stunning tee-shot on the third had Woodland into double-figures but he bogeyed the next and Kisner led on his own after a six-footer on the seventh.
Woodland made the most of the par five eighth and when Kisner missed the green on the ninth, he was left with 23 feet for par and a 63 - which he missed.
Koepka had less than five feet for birdies on the 13th, 15th and 17th and the dialled-in iron play continued in a hat-trick of birdies from the first. He made the most of the eighth but could only par the last after being faced with 20 feet for a 62.
A hot putter handed Schwartzel a birdie-birdie start but he bogeyed the sixth before bouncing back with birdies on the seventh and eighth. The 2011 Masters Tournament winner made a hat-trick of his own from the tenth and a stunning tee-shot on the 16th set up a birdie and his chance at history from 50 feet on the last.
Pieters was bogey-free as he fired his lowest round in a Major, making nine pars on his first nine before birdieing the first, fourth, seventh and eighth.
Johnson was one over par after 11 holes but birdied five of his next six to storm back into contention.
Stone made three birdies and a bogey to sit a shot ahead of a strong group containing Open champion Francesco Molinari, two-time Rolex Series event winner Jon Rahm, 2013 Masters champion Adam Scott and Americans Patrick Cantlay and Jason Kokrak.