Oosthuizen had a bogey on his final hole but is still at 13-under 206 for the tournament. Brier shot 3-under 70 Saturday to keep a share of the lead.
Jbe Kruger had a 6-under 67 Saturday and is tied with Manuel Quiros (68 Saturday), Charl Schwartzel (68) and Jaco Van Zyl (7-0) for third at 12-under. Four more golfers, including Branden Grace (72) and Miles Tunnicliff (72), who were tied with Brier for the second-round lead, are two strokes off the leaders' pace.
Brier's third round included back-to-back birdies at Nos. 3 and 4 and a bogey at the 16th hole. He also posted an eagle on the 527-yard, par-5 11th hole for the third consecutive day.
Oosthuizen opened with three birdies in his first six holes but had a bogey at the ninth hole. He got that stroke back with a birdie at the 12th hole and went to 5-under on the day with an eagle 3 at the 545-yard 15th hole. He slipped into a tie for first with the bogey at 18.