Austin Cook carded an eight-under 62 to take a one-shot lead at the RSM Classic, pulling clear with Brian Gay Friday.
Playing the Seaside course at the Sea Island Golf Club, Cook holed four birdies on the front and back nines in his second round.
The American's 62 saw him move into 14 under, a shot ahead of Gay - who fired a 64 on the same course.
The duo have pulled clear at the halfway mark of the PGA Tour event at St. Simons in Georgia.
C.T. Pan, playing the Plantation course, fired a seven-under 65 to sit at nine under, tied for third with Chris Kirk (70, Seaside course) and Vaughn Taylor (66, Seaside).
A group of six players are a shot further back at eight under, including Brendon de Jonge.
The Zimbabwean has missed 18 of his last 19 cuts, but is in contention after back-to-back 67s.
Brandt Snedeker, Ben Silverman, Andrew Landry, Blayne Barber and Brice Garnett are also tied for sixth.
Defending champion Mackenzie Hughes missed the cut, as did 2014 winner Robert Streb.