A five-under-par 66 gave Colt Knost a two-stroke lead at the halfway mark of the RBC Heritage on Friday.
The American, who shared the lead overnight, had three birdies in a four-hole stretch as he finished on nine-under 133 at Harbour Town Golf Links in Hilton Head, two strokes clear of Carl Pettersson, who shot a 65, and three shots ahead of Boo Weekley (66), a two-time winner of this event, and Harris English (68).
Joint first-round leader Chad Campbell (70) follows on five under alongside Robert Garrigus (66), while defending champion Brandt Snedeker had five consecutive birdies on the way to a 67 and was tied with Michael Bradley (64), Kevin Na (68), Bob Estes (67) and Fredrik Jacobson (67) at four under.
World No 1 Luke Donald, one of the few big names in attendance this week, struggled on day one, carding a disappointing 75, but bounced back with a two-under 69 in the second round to make the cut. At one over par he is still ten shots off the lead, however, and the Englishman needs a top-eight finish to hold on to his position atop the world rankings list.
Knost's round got going with a stretch of three birdies in four holes to give him the lead at eight under. He made his final birdie on the par-five fifth and finished his round without making a single bogey.
"I felt so comfortable out there being around the lead, even though it's only Friday," he said. "I think I'm also going to feel great this weekend."
Pettersson's 65 was his lowest round at Harbour Town in the eight years he's played there.
"My game is good," he said. "In golf, you still have two days, which is a long way to go."
A couple of notables missed the cut, including last year's FedEx Cup champion Bill Haas, and a pair of three-time major champions in Padraig Harrington and Ernie Els.
Els, who missed the Masters last week after failing to qualify, shot an 8-over 43 on his final nine holes, including a triple-bogey 7 on the 18th.
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