George Coetzee fired a bogey-free 64 to set the clubhouse target on day two of the Tshwane Open.
Pretoria Country Club is Coetzee's home course and despite saying earlier in the week that it does not always suit his game, he followed up his opening 67 to get to 11 under as he searches for a second title at this event.
Finn Mikko Korhonen matched his 64 to sit a shot off the lead alongside resurgent Chilean Felipe Aguilar, who fired a 67.
The duo were then three shots clear of overnight leader Louis de Jager - who was among the later starters - with the players in the afternoon left with some work to do to reel them in.
Aguilar lost his card last season but regained it at the Qualifying School to make it 11 uninterrupted campaigns on the European Tour, although he did miss his first three cuts in 2018.
Korhonen, meanwhile, was a runner-up here last season and is looking for his first European Tour title.
Aguilar picked up birdies on the third, fifth and seventh before eagling the par five ninth to get to 11 under and lead by one from Coetzee at the turn.
The South African - who started on the tenth - made four gains in a row from the 12th and added to them on the 17th and 18th.
Korhonen had birdies on the 12th, 13th, 14th, 16th and 18th and, while he dropped a shot on the first, he regained it at the third.
A run of pars followed from the three leading contenders but a poor second shot left Aguilar in a nasty lie on the 13th and his chip went a long way past the pin to lead to a first bogey of the day.
Korhonen then put his approach to the par five ninth to five feet and made an eagle to make it a three-way tie at the top.
Aguilar got his nose in front with a birdie on the 15th but Coetzee put his tee-shot on the par three eighth to four feet to join him at 11 under.
Two-time European Tour winner Aguilar found sand off the 18th tee to surrender a second bogey of the day and drop alongside Korhonen.
Home duo Christiaan Bezuidenhout and Erik van Rooyen were then in the clubhouse at six under alongside Scotland's Scott Jamieson.
Bezuidenhout made bogeys on the 12th and 16th but fought back with gains on the 18th, fourth, seventh and ninth.
Van Rooyen - who could win the Sunshine Tour Order of Merit this week - also had a slow start and was level par after 15 holes but hit a stunning approach into the seventh for a birdie and made a closing eagle to vault himself back into contention.
Jamieson birdied the 16th and 18th but bogeys on the fourth and fifth dropped him back before he picked up shots on the sixth and ninth.
England's Laurie Canter - a Qualifying School graduate for the past three seasons - was another player to equal the lowest round of the week with a bogey-free 64, making birdies on the second, fourth, fifth, seventh, 11th, 14th and last.
Countryman Matthew Baldwin, Swede Christofer Blomstrand and South Korea's Jinho Choi were also in the clubhouse at five under.
Major champion Danny Willett was a further shot back after a 68 - his first sub-70 round since returning from a shoulder injury - had him on course to make a first cut of the season.
