Jordan Spieth bounced back from a Masters hangover by firing a nine-under second round, but is still well behing the lead at the RBC Heritage in South Carolina.
Fellow American Troy Merritt went one better than Spieth with a record-tying 61 to take a four-shot lead.
Merritt made seven birdies on the back nine, closing with four in a row to match the course record round set by South African David Frost in 1994 for a 36-hole total of 12-under-par 130 at Harbour Town Golf Links.
"I had my tempo down the stretch, especially with the irons. It was fun to see the putts roll in," said Merritt.
But Merritt, who carded a 28 on the back nine, cautioned he was only halfway through the tournament.
"I plan to enjoy the moment, hit some good shots, not think about it too much and just add them up at the end of the day."
Tied for second at eight-under 134 were defending champion Matt Kuchar (66) and John Merrick (65), with 2013 winner Graeme McDowell of Northern Ireland (69), 2010 champion Jim Furyk (64) and Kevin Kisner (67) another shot away on 135.
Climbing into contention earlier in the day was Spieth, who struggled to a 74 in the opening round after a whirlwind New York media blitz following his Masters triumph.
He improved by a dozen strokes on a warm, wind-free day with nine birdies in a flawless round at Hilton Head.
"I found something in my ball position on the range and it made a world of difference," said the 21-year-old Texan, who was six strokes off the lead.
"One more night's sleep and just feeling like I had a little something that I could think about on the course helped me zero in on targets a little better.
"I didn't want to go home early."