Gary Woodland fired the lowest 36-hole total in US PGA Championship history before storms saw play suspended for the day during round two at Bellerive Country Club.
The American fired a 66 to take his record low-total to a ten under par 130, one shot clear of countryman Kevin Kisner.
Two-time defending US Open champion Brooks Koepka was eight under after equalling the lowest round in US PGA Championship history with a 63, a feat matched by South Africa's Charl Schwartzel who was a shot further back.
Belgian Thomas Pieters and World Number One Dustin Johnson were also in the clubhouse at seven under alongside Rickie Fowler, who had played ten holes when the horn sounded at 3.35pm local time and brought the players off for the day.
Play will resume at 7.00am on Saturday with some groups left with 14 holes to play, and round three will then begin 30 minutes after the conclusion in three-balls off the first and tenth tees.
Woodland has never had a top ten in 29 Major appearances but he does have three US PGA Tour titles to his name - including this season's Waste Management Phoenix Open.
"I probably didn't play as well as I did yesterday top to bottom but the iron game really kept me in it today," he said. "I got a little wayward with a couple of drives and hit a lot of good putts that didn't go in so I can live with that.
"For me, I'm very happy with where I'm at. I'm very comfortable with how I'm driving the golf ball. The iron game, the distance control this week has been phenomenal. And when I stand over a golf ball putting as comfortable as I am right now, I'm pretty excited."
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 attempts 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.
South African Brandon Stone made three birdies and a bogey to sit at six under, 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.
Pat Perez was in the group at five under having played nine holes, while 14-time Major champion Tiger Woods birdied three of his first seven holes to get to three under.