Charl Schwartzel fired a stunning 63 to set the clubhouse target on day two as he seeks an elusive first win at the South African Open hosted by the City of Johannesburg.
The South African has claimed eight of his 11 European Tour wins on home soil but his national Open has so far eluded him, with two runner-up finishes and a further four top fives.
An opening 67 on the tougher Firethorn Course gave the 2011 Masters Tournament winner an excellent foundation at Randpark Golf Club and he built on that brilliantly over the Bushwillow in round two to move to 12 under.
That gave him a one-shot lead over Zambia's Madalitso Muthiya, with last week's winner Kurt Kitayama and Qualifying School co-winner Zander Lombard at ten under.
South African Jbe Kruger was in the clubhouse three shots off the lead.
Kitayama quickly picked up where he had left off on Thursday with a birdie on the first on the Bushwillow to join the lead and it was soon a three-way tie as Muthiya made a gain on the fourth on the Firethorn.
A first bogey of the week from Kitayama on the sixth dropped him out of the lead but he bounced straight back on the next, with Muthiya then dropping his first shot on the eighth.
The 35 year old produced a bounceback of his own, however, making a gain on the ninth to once again make it a three-way tie at nine under alongside overnight leader Louis Oosthuizen.
Kruger started with a bogey but then birdied the second, fourth, eighth and ninth to turn in 32 on the Firtehorn before bogeying the tenth and birdieng the 13th.
Better was to follow and the 32 year old eagled the par-five 14th but a bogey on the next dropped him into a five-way tie at the top.
The 12th on both the Firethorn and the Bushwillow are par fives and Kitayama and Muthiya took advantage to edge ahead but a double-bogey after a three-putt on the next slipped Muthiya back.
He recovered in brilliant fashion, birdieing the 14th and 15th and when he made a 12-footer on the 16th, he led alone at 11 under as he one-putted his final five holes.
A Kitayama bogey on the 16th extended the lead to two shots but he bounced back after finding the green at the par-five 17th in two.
Up until that point Schwartzel had been quietly compiling a handy score, birdieing the first and fifth to turn in 33 and adding further gains on the 11th, 12th and 14th.
A long putt on the 16th had him within one but a poor tee-shot meant he had to lay-up ahead on the 17th. That proved no problem as he hit his third into the back fringe and spun the ball back into the cup for an eagle and the lead.
Lombard produced a brilliant opening 64 on the Firethorn but was in danger of squandering that when he paired three birdies on the front nine with a bogey on the second and a triple on the third to turn in 36.
Birdies on the 11th and 12th moved him back into red numbers and he got on the green in two at the 17th to make an eagle and get within two.
Zimbabwean Mark Williams was at nine under with three holes to play, a shot clear of Branden Grace, Oosthuizen, David McIntyre and Bernd Ritthammer - who were all out on course.