George Coetzee edged one shot ahead of English pair Richard Finch and Robert Rock after six holes of the Joburg Open third round.
All three had gone into the round holding the joint lead on 11 under and they looked set to continue that as they each birdied the first hole.
But as Finch and Rock both dropped shots it was left to South African Coetzee to take the outright lead.
Rock was the first to falter on the third but when Finch also failed to make par on the fourth Coetzee again held his to keep the advantage.
Things had looked good for Finch on the opening hole as he claimed a birdie and he was joined by both Rock and Coetzee – getting down in two from on or around the green at the par five.
All three made par on the second but Rock paid for a short approach shot on the third and dropped a shot, Coetzee making par and Finch seeing his birdie putt lip out.
Coetzee made par on four, but when Finch dropped a shot he joined a group of six, including Rock and Retief Goosen, on 11 under.
Finch just failed with a birdie putt on the par three fifth as both Rock and Coetzee made par.
Coetzee went two ahead on the par five sixth hole he when kept his nerve to make a birdie after his eagle putt from near the back edge of the green was well short.
Rock held on for a scrappy par, but Finch cut the lead back to one when he rolled in a birdie to go to 12 under, one behind Coetzee.
Rock was joined on 11 under in a group of seven by Scotland's David Drysdale and South Africans Goosen, Jean Hugo, Michiel Bothma, Branden Grace and Shaun Norris.
