Jason Dufner equalled the lowest round in major championship history, after coming up woefully short with a putt to claim the outright record in the US PGA Championship at Oak Hill.
Dufner needed to hole from 12 feet on the 18th to card an eight-under-par 62, but left his birdie putt well short of the hole and had to settle for "only" a course-record 63.
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, who finished nine under par to lead by two from Masters champion Adam Scott and American pair Jim Furyk (68) and Matt Kuchar, who carded a 66 after dropping his first shot in two days on the 18th.
"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 name 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, 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."
Graeme McDowell is best of the Irish on one under, while Rory McIlroy is level par at the half-way stage.
Shane Lowry is another shot back, one shot clear of Darren Clarke who also made it through to the weekend on two over.
Padraig Harrington missed the three-over cut on seven over, as did fellow Dubliner Paul McGinley who finished the tournament on 12 over par.
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 become the first player to capture a major with a long putter.
Simpson, who became the second the following June at the US Open, 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 20ft 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 Sweden's Henrik Stenson and playing partner Justin 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 10th 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 15ft.
"I sit here today really relishing the opportunity on the weekend to try and 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 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."