George Coetzee stretched his advantage at the Tshwane Open to two shots ahead of round four, while Sam Horsfield surged up the leaderboard on Saturday.
Home favourite Coetzee, champion in 2015, led by one after Friday's second round and a three-under 68 left him on 14 under for the tournament, two clear of Horsfield and Mikko Korhonen.
Coetzee, a three-time European Tour winner, would have been in an even better position had he not bogeyed the par-five 18th.
Horsfield's round of 64 was his lowest in a professional event, and the Englishman backed up a flying start that saw him begin with four straight birdies by making further gains at the ninth, 11th and 12th in a blemish-free 18.
Korhonen, runner-up last year, was one of two players just one shot shy of Coetzee before the start of play, but he is now another stroke off the pace after battling back from two over through 11 to finish two under for the round.
Felipe Aguilar fell back to four shots off the lead, the Chilean enduring a mixed round en route to a level-par 71 that left him in a four-way tie for fourth.