A pair of early eagles and a strong finish saw Jason Dufner claim a one-shot advantage over Graham DeLaet at the RBC Heritage, as Luke Donald's hopes of victory were dented.
Dufner began Saturday three shots off the pace set by DeLaet and Donald, but moved to the top of the leaderboard at 13 under courtesy of the low round of the day, a six-under 65.
An eventful start to Dufner's round saw the winner of the 2013 US PGA Championship record two eagles and two bogeys in his first five holes.
He then dropped a shot at the seventh, but birdied nine and 10 before picking up further shots at the 14th, 15th and 16th to claim sole possession of the lead.
DeLaet duly made his fourth birdie of the day, at 15, to move alongside Dufner. However, a bogey at the last saw the Canadian – still winless on the PGA Tour – sign for a 69 and slip back into second.
Webb Simpson and Ian Poulter each held the lead at one stage, only to end their respective rounds two and three shots behind.
Simpson turned in 32, but came back in one over to share third at 11 under with Kevin Kisner, who carded a bogey-free 66.
Poulter, playing on a medical extension, matched Simpson's front-nine score before double-bogeying the 10th and dropping another shot on 11. A birdie at 14 ensured the Englishman went round in 69 to sit fifth.
It was a frustrating day for Poulter's compatriot Donald, a player who has finished second or third in six of his last eight visits to Hilton Head.
Donald could only muster one birdie in a 72 that leaves him four behind with 18 holes to play.