Louis Oosthuizen extended his lead to five shots to put himself firmly on course for a first victory at the South African Open hosted by the City of Johannesburg.
The home favourite has a Claret Jug and has claimed four of his eight European Tour victories in South Africa, but a national Open title is still missing from the 36 year old's CV.
He saw his three-shot overnight advantage cut to one as he made a shaky start but four birdies in six holes saw him turn in 33 and get to 16 under.
Zambia's Madalitso Muthiya was the closest challenger, a shot clear of eight players at ten under.
Oliver Wilson made a fast start with birdies on the third and fourth and hit an excellent approach into the sixth to get to nine under.
Branden Grace birdied the first with a long putt but gave the shot straight back before making another gain from 15 feet at the third.
Oosthuizen recovered from a poor tee-shot on the first to make a par but Muthiya dropped a shot and roles were reversed on the second.
Another poor tee-shot from the leader this time led to a dropped shot, while Muthiya made a gutsy 15-footer to save par.
Grace then broke out of the group at nine under with a 20-footer on the fifth.
A poor second shot from Muthiya saw him surrender a bogey on the third and with Oosthuizen going right off the tee and failing to get up and down from the sand, the lead was down to two.
Grace hit a stunning approach to tap-in range on the sixth and he was all of a sudden just a shot back.
A five-footer on the ninth got Wilson into double figures and Muthiya fought his way back, with a nice chip on the fourth and a putt from the fringe on the next bringing a pair of birdies.
Oosthuizen briefly extended his lead back to two with a birdie on the par-five fourth but Grace hit an approach to eight feet for a birdie on the seventh before surrendering a three-putt bogey on the next.
An approach to six feet on the sixth then moved Oosthuizen back to where he had started the day - 14 under and three clear.
A long double-breaker on the seventh brought another gain and after a rocky start, the 2010 Open Champion was in total control.
Wilson took advantage of the 12th to join that group at 11 under but the Englishman gave the shot straight back, with Grace also slipping five off the lead with a bogey on the tenth.
That group was soon six back as Oosthuizen drove the ninth green and two-putted to turn in 33 and get to 16 under.
South Africans Thomas Aiken, Bryce Easton, Jbe Kruger, Charl Schwartzel, and Haydn Porteous were at ten under alongside Grace, Wilson and Frenchman Romain Langasque.