Wallie Coetsee continued his fine start to the Joburg Open as a six-under 65 left the home favourite one shot clear after round two.
Coetsee opened his tournament with a 66 on Thursday on the East Course and followed up with another excellent display on the Royal Johannesburg and Kensington's West Course on Friday.
The South African blitzed four birdies in the opening six holes and a bogey at seven proved the only blip on the front nine.
An eagle at the par-five 15th further boosted his score and he picked up another shot at 17 to ensure he takes the outright lead into the weekend.
"I made one stupid bogey out there on the seventh, but I enjoyed the round a lot," said Coetsee.
"There were a few sucker pins out there, so I went for middle green. I didn't attack too much and just stayed calm, which paid off.
"This is a marathon, not a race [sprint]. You have to pull the horse back a bit, you can't run too fast. We'll let the horse loose on Sunday on the back nine."
Englishman Simon Dyson shot six birdies and carded a solitary bogey as he signed for a round of 67 to join a three-way tie for second.
Coetsee's South African compatriots Garth Mulroy and Tjaart van der Walt are also on 11 under for the tournament, while Niclas Fasth and Anthony Wall are a further shot off the pace.
Overnight leader Nic Henning started with a tournament-equalling 62 on Thursday, but the world number 1,555 endured a miserable day on the East Course and a six-over-par 78 meant he missed the cut after slipping to three under for the tournament.