Alexander Bjork kept a share of the lead and was joined on 10 under by Scott Jamieson on Friday after two rounds of the Tshwane Open.
They lead James Morrison by one stroke, with three players a shot further back in a tie for fourth.
Bjork (67) is playing in only his ninth European Tour tournament and is seeking a first victory. The Swede made six birdies at Pretoria Country Club to go into the weekend with a good chance of a maiden title.
Jamieson (65) kick-started his round with four birdies in five holes from Nos. 5-9.
Thomas Aiken had the round of the day, a 9-under 62 with 10 birdies, to move into the tie for fourth.