Golf:Former American Walker Cup player Colt Knost was the early clubhouse leader after shooting a 66 on the second day of the RBC Heritage in South Carolina.

While Knost held a two-shot lead over Carl Petterson, Luke Donald was three under after 12 holes and one over for the tournament 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 yesterday but had improved early today with three birdies in a bogey-free round. A bogey on the par-five 15th saw him slip back to two over, but he made par on the final three holes to card a 69.

Knost started the day in a three-way tie for the lead with Chad Campbell and Vaughn Taylor.

He 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 yesterday’s 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).

Pádraig Harrington failed to make it to the weekend after he carded a one-over 72 to finish on four over, one shot outside the cut.