Nick Watney fired an eight under par 62 to set a new course record and take the joint lead heading into the final round of the AT&T National in Pennsylvania.
KJ Choi had equalled the then course record of 64 in round two before Chris Kirk lowered it by one early in round three. Minutes later Steve Marino equalled that but then, less than an hour later, Watney set his own mark.
The American had fired unspectacular rounds of 70 and 69 but today he needed just 27 putts to complete the round at Aronimink.
Watney had a perfect start, sinking two straight birdies before two bogeys at the end of the front nine.
However, he had a superb second nine, putting six birdies and an eagle to take a joint lead with Rickie Fowler at nine under heading into the final round.
"I guess anything is possible," Watney said. "But I don't think you ever expect to shoot that low.
"You don't go on to the golf course very often anticipating a 62."
Fowler ensured co-leader status by shooting six birdies in his opening ten holes on his way to a 64.
Earlier Kirk had set a new mark after a seven under par 63, needing just 24 putts to complete his round.
The American sunk two birdies on his first two holes with three more on the front nine before a further three on the way back and just one bogey.
However, Marino then equalled the new record with a 63 of his own.
Five birdies on the front nine, including four out of five from the fifth, were followed by four more with two bogeys the only blemish.
Fowler and Watney finished the day one shot ahead of overnight leader Choi, who birdied two of his last three holes on his way to a 69.
Marino, Adam Scott (66) and Webb Simpson (64) were two shots behind at seven under.
