Carl Pettersson (Getty Images)
Sweden’s Carl Pettersson moved into second place as Colt Knost became the halfway leader after shooting a five under par 66 on the second day of the RBC Heritage in South Carolina.
While Knost on nine under held a two shot lead over Pettersson, Luke Donald made the cut at two over with a two under round of 69 as he looks to retain his World Number One slot.
The Englishman needs to finish in the top eight at Harbour Town to remain ahead of Ryder Cup team-mate Rory McIlroy in the standings.
He struggled to a four over par 75 on Thursday but improved early on with three birdies in a bogey-free first seven holes.
He finally dropped a shot at the 15th though, leaving him six shots off the top-eight finish he needs.
Knost started the day in a three-way tie for the lead with Chad Campbell and Vaughn Taylor.
The American made an ideal start with birdies at the first two holes before finishing a bogey-free round with five birdies overall.
Pettersson hit three consecutive birdies, and seven in total, as he followed up an opening 70 with a 65, although it could have been even better if he had not bogeyed the 15th.
Boo Weekley and Harris English were a further shot back after rounds of 66 and 68 respectively while Campbell (70) had slipped to a tie for fifth with Robert Garrigus (66).
Taylor hit four bogeys in his 73 to slip to a tie for 16th.
Defending champion Brandt Snedeker hit a 67 to sit four under in a tie for seventh, with England's Gary Christian one stroke back following his 68.