US TOUR:COLT KNOST was the early clubhouse 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 Carl Petterson, Luke Donald, looking to retain his world number one slot, finished on three over after a round of 69.

The Englishman needs to finish in the top eight at Harbour Town to remain ahead of Rory McIlroy in the standings.

Having struggled to a four-over-par 75 on Thursday, he enjoyed three birdies on the front nine yesterday but bogeyed the par-five 15th to finish well down the field.

Pádraig Harrington missed the cut after a 72 left him on four over.

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.

Petterson hit three consecutive birdies, and seven in total, as he followed up Thursday’s 70 with a 65.

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 15th.

Early second round scores (par 71): 133: C Knost (67, 66); 135: C Pettersson (70, 65); 136: B Weekley (70, 66), H English (68, 68); 137: C Campbell (67, 70), R Garrigus (71, 66); 138: F Jacobson (71, 67), B Estes (71, 67); 139: C Hoffman: 74, 65), Z Johnson (71, 68), B Cauley (71, 68), G Christian (71, 68)