Robert Streb fired a record-equalling 63 to take a share of the second-round lead alongside Jimmy Walker on a dramatic day at the US PGA Championship.
There has never been a 62 in a Major Championship but Streb made the 30th 63 and the third in 15 days after Phil Mickelson and Henrik Stenson both equalled the mark at The Open Championship.
Streb and Walker's totals of 131 also equalled the lowest 36-hole score in US PGA Championship history as the duo moved to nine under at Baltusrol Golf Club, two shots clear of defending champion Jason Day and Emiliano Grillo.
Day had threatened to steal the show as he made seven birdies in eight holes from the eighth to surge up the leaderboard but Streb made three gains of his own in his last four to move to the summit.
"I'm sure it will be busy, Saturday at a PGA," said Streb. "But I'll just try to stick to what I'm doing. Try to do the same things we've been doing the last couple of days and hopefully it's good enough.
"I'll just try not to get too hung up in what's going on and try to stick to the golf and see if I can have a little fun while I'm at it.
It was a great round. I'm happy to be a part of that 63 club - Robert Streb
Open champion Stenson was at six under, a shot clear of 2010 champion Martin Kaymer, Patrick Reed and Brooks Koepka.
Torrential overnight rain and further wet weather in the morning had led to an early delay of 40 minutes and softened the course up, making conditions more favourable for the later starters.
Stenson was among the morning starters and recovered from two early bogeys to fire a second consecutive 67, the catalyst for which was a stunning eagle as he put his approach on the 18th to three feet.
Walker and Grillo then went toe-to-toe in the early afternoon, with the Argentinian turning in 32 after starting on the tenth and Walker adding a hat-trick of birdies from the 12th to gains on the fifth and eighth to get to double figures.
Streb, meanwhile, turned in 33 with four birdies and a bogey, adding another gain on the second to join the chasing pack.
Day made a double-bogey on the seventh to sit two over for his round before he went on his remarkable run, with putts of 18, 19 and 37 feet on the tenth, 13th and 14th, but he could not take advantage of the closing par fives to close the gap further.
A bogey on the last from Walker dropped him to nine under and a 21-foot putt on the ninth - his last - completed Streb's big finish.
"I felt like I could go out and shoot another good score," said Walker. "I saw what the weather was going to do and knew that it was going to be out there to play good. If you hit the shots, you knew it was going to be there for you to make some birdies.
I was exblockquoted to go play today, I really was. I was nervous but exblockquoted. I'm real happy with today - Jimmy Walker
Kaymer also had three birdies in his last four holes in a 69, while Reed carded a 65 and Koepka a 67.
Welshman Jamie Donaldson signed for a 67 to sit at four under, a shot clear of World Number Three Jordan Spieth and Frenchman Grégory Bourdy.
Two-time champion and World Number Four Rory McIlroy responded to his opening 74 with a 69 but a bogey on the last saw him miss the cut by one stroke.
