Jason Dufner shot a Major Championship record–equalling 63 to grab the halfway lead at the US PGA Championship.
The American became the 24th player to achieve the feat, moving to nine under par at Oak Hill and two clear of compatriots Matt Kuchar and Jim Furyk and Masters Tournament winner Adam Scott.
England’s Justin Rose and in-form Swede Henrik Stenson lead the European challenge a shot further back on six under going into the weekend.
Dufner needed to hole from 12 feet on the 18th to card an eight under par 62, but left his birdie putt well short.
It was the 26th such score recorded in a Major and came just hours after Webb Simpson had equalled the previous course record of 64 set by Ben Hogan in 1942 and matched by Curtis Strange in the 1989 US Open.
"It's tough," said the 36 year old. "I showed a little bit of nerves there leaving it short. It's one you would like to gun and have a chance at history but it was probably the worst putt I hit of the day, which is a little disappointing.
"But all in all it's a 63 and my name is on top of the leaderboard, so that's a great position to be playing from. To join history, to shoot a 63 in a Major, it’s pretty unbelievable.
"The history of the game is something that is dear to my heart. To be part of history is a neat accomplishment. I never thought a guy from north-east Ohio would be able to do these things. Hopefully it will propel me to a great weekend."
In the final round of the 2011 US PGA, Dufner led by five shots after nearest challenger Keegan Bradley triple bogeyed the 15th, only to find water on the same hole minutes later. After doing well to escape with a bogey there, he failed to get up and down from sand on the next and then three-putted the 17th.
Both men parred the 18th to go into a three-hole play-off which Bradley won by a shot to win on his Major Championship debut.
Simpson, who the following June at the US Open Championship, was seven under par after 15 holes and needed to play the last three in one under to shoot 62, but could only manage a bogey and two pars.
Dufner carded an eagle on the second and three birdies to be out in 31 and picked up further shots at the 11th, 13th and 16th before agonisingly missing from 20 feet for birdie on the 17th.
"I hit a great putt there," added Dufner, who was playing with the last man to shoot 63 in a Major, Steve Stricker doing so in the 2011 US PGA. "I thought that one was going to go in. I didn't think the one on 18 was going to go in when it came off."
Scott added a 68 to his opening 65 to finish one ahead of Stenson and playing partner Rose, who shot a stunning 66 thanks to a brilliant homeward nine of 29.
US Open Champion Rose admitted he had been "hanging on for dear life" after starting on the tenth and dropping shots at his first two holes, but after reaching the turn in 37 the Englishman stormed home in 29 with six birdies - the longest coming from 15 feet.
"I sit here today really relishing the opportunity on the weekend to try to win another Major with no hesitation, which there may have been a few years ago because you don't know how it's going to pan out or how you're going to deal with it," said Rose, who finished fourth in The Open as a 17 year old amateur in 1998 but then missed 21 cuts in a row after turning professional the next day.
"It's wonderful to be in this situation right now, talking about having done it, talking about feeling like you can win more, believing in yourself and not talking about how I hope it could happen this week. So I think that alone makes it easier."
Only golfing greats Gene Sarazen (1922), Ben Hogan (1948), Jack Nicklaus (1980) and Tiger Woods (2000) have won the US Open and US PGA in the same year, while Nicklaus was also the last man, in 1975, to win the Masters Tournament and US PGA in the same season.
That is Scott's aim after he claimed his first Major title at Augusta National in April, the Australian having also finished third in The Open at Muirfield last month.
"I think the platform has never been better for me to go on and win multiple Majors," said Scott, who sent his good friend Rose a text saying 'This is our time' after his Masters triumph.
"I guess you've got to take the confidence and form of winning a Major and run with it. I was hungry before the Masters and I might even have a bigger appetite after it. It might be greedy, but I feel like this is my time to get everything I want out of my career and I'm going to keep pushing until I do.
"I've got to take advantage of it, otherwise it's all a waste."
German Ryder Cup hero Martin Kaymer and Australia’s Marcus Fraser will also be flying the flag for The European Tour over the weekend after respective rounds of 68 and 69 left them on four under and inside the top ten.
“The putter has been rolling pretty good, so hopefully that continues over the weekend,” said Fraser, who has never finished higher than 35th in a Major Championship.