Troy Merritt shot a course record-equaling 61 to open up a four-shot lead after the second round of the RBC Heritage.
For much of the day, Matt Kuchar looked set to take the lead into the weekend, but that was before Merritt stole the show with a scintillating back-nine performance late in the afternoon.
Three under par for his round when he reached the turn, the 29-year-old added seven more birdies in his final nine holes, including four in a row from the 15th.
That was good enough to equal David Frost's 21-year-old Harbour Town Golf Links course record.
Earlier, Masters champion Jordan Spieth, playing alongside Kuchar, stole the limelight with a nine-under-par 62 which lifted him 86 places into the top 10.
"That was just better golf," said Spieth, who admitted after shooting a 74 on Thursday that he had an off-day. "I told you guys yesterday, no excuses. I just played poorly."
"I went back to posture, ball position, hand position and tempo," he explained. "And I struck that ball quite a bit better."
But for Merritt's heroics, Spieth would have been just two shots off the weekend lead. As it stands, he's six back with two rounds remaining.
"Any time you can match the reigning Masters champ shot for shot, it's pretty cool," said Merritt, who is still chasing his first PGA Tour victory after seven years on tour.
Merritt played his round in front of a sparse gallery, with most spectators following the Spieth and Kuchar pairing, but he got a standing ovation after his birdie at 18 equaled the record.
"Usually, when I see the (large) crowd like that, it's because I'm in them," he quipped.
Kuchar lies in second place, four back, after a 66. He's tied with John Merrick, while Jim Furyk, Graeme McDowell and Kevin Kisner follow a further shot back on seven under.
Major champions Spieth and Louis Oosthuizen lie on six under, along with Morgan Hoffman, Kevin Streelman and Arnold Palmer Invitational champion Matt Every.
"It was cool to see, just huge crowds," Kuchar said. "People (were) really excited to see the defending Masters champion. And then the fact that both of us got going pretty well today, there was a lot of excitement, a lot of people coming to check it out.
"And it was every bit a weekend feel, a major feel. It had great buzz."
Golf365.com