An unblemished 65 from Englishman Steve Webster saw him surge into Joburg Open contention, with Wallie Coetsee leading the way by two after three rounds.
Coetsee's modest 70 - five worse than he managed on Sunday - was actually enough to extend his overnight advantage at the summit by one stroke.
But, while the South African's nearest challengers at the start of the day faded - with Simon Dyson and Garth Mulroy going around in par, and compatriot Tjaart van der Walt shooting 71 - Webster found his best form.
Elsewhere in the field, another of the home-grown contingent endured a miserable outing, with Allan Versfeld - who shot 67 in the second round - carding an error-strewn 81.
Coetsee started slowly on the East Course, which exclusively hosts the weekend's action having been used in tandem with the West Course over the first two sets of 18.
He was one over until scoring a three on the par-four ninth, while three consecutive gains from the 11th lifted him away from the chasing pack before a dropped shot at 16 and a closing birdie.
For Webster, a birdie at the first set the tone for a front nine that saw him pick up five shots, with a further two in the final three holes wrapping up the best round of the day.
"I made a good birdie at the first and a good save at the second and just got on a bit of a roll," Webster told the European Tour website. "I missed three or four 12-footers which was frustrating but there was a lot of really good golf.
"I gave myself a lot of chances and that's what my game is all about."