Nick Doughetry, Rolf Muntz and Gary Murphy stand four off the pace at 6-under-par 138. Dougherty tied the course record with his 6-under 66.
A threesome of South Africans make up a group that sits at 5-under par, five in back of Clark, and includes overnight leader Jean Hugo. Hugo struggled home on Friday with a 1-over 73.
Clark, taking advantage of the absence of fellow compatriots Ernie Els and Retief Goosen, is looking like the man to beat in his host country's Open championship. He goes into the weekend with a small but comfortable advantage, and also the knowledge that comes with being the defending champion.
Though giving back a shot to par on the par-5 16th, his only bogey of the tournament, Clark had a shot to give after a wonderful eagle at the 13th. Using a fairway wood, he knocked his approach to 20 feet and rolled home the putt for an eagle-3 and moved to three clear of the field.
'I feel pretty comfortable,' said Clark. 'I am eliminating mistakes and one bogey in 36 holes isnt bad.:'
Coltart (69) and Lawrie (69) matched each other's score for the second consecutive day as they both moved into contention.
Coltart had six birdies on the day, but a bogey and a double bogey on the front side cost him a possible share of the lead. Still, he was happy with the result.
This winter Ive possibly done the least work on my game and had the most fun,' Coltart said.
Lawrie, who won the Challenge Tour Grand Final, the European developmental tour's season-ending championship, enjoyed four birdies and a late bogey as he heads into quite possibly the biggest golf weekend in his career.
As for the weekend, I wont be looking at anyone else. I havent played in front of big crowds before and I am looking forward to being in the last group, but I dont think it will bother me, a relaxed Lawrie mused.
England's Justin Rose, perhaps the pre-tournament favorite, carded three birdies and no bogeys to move to 3-under and into a tie for 15th. Though seven strokes back, look for Rose to make up some ground come Saturday and Sunday.
Lee Westwood backed up his opening-round 75 with a dismal 77 that knocked him from play on the weekend. Three bogeys and two double bogeys kept the 2000 Order of Merit winner on his continual free-fall from the game's elite.