Fichardt eagled the third hole en route to a 7-under 65 that gave him a share of the lead with Van Zyl at 15-under 201 heading into Sunday's final round.
Van Zyl finished the day with a 4-under 68 that included five birdies and a bogey.
Second-round leader Adilson Da Silva of Brazil fell into third place at 13-under after carding a 1-over-par 73.
Frichardt had no such trouble with the East London Golf Club links. He opened the day with a birdie followed by a 20-foot eagle putt on No. 3. A bogey 17 prevented him from taking sole possession of first place.