Oosthuizen finished his first nine of the second round with three consecutive birdies and the fast close at 17 and 18 gave him an 8-under-par 64. He is at 12-under 132 after 36 holes.
That's just better than first-round leader Thongchai Jaidee and Scott Jamieson, who are tied at 11-under. Jamieson, despite a bogey, matched Oosthuizen's 8-under score Friday. Jaidee had an eagle and a bogey in a 4-under 68 in his second round.
Six players are tied for fourth at 5-under 139, seven strokes off the lead.
Oosthuizen had three bogeys in his first-round 68 but was bogey-free Friday. He posted back-to-back birdies at Nos. 3 and 4 before ending the front nine with birdies over 7, 8 and 9. He added another at the 13th hole before the closing birdies at the par-4 17th and 18th holes.
A total of 33 players are in the Volvo Golf Champions event. Players earned invitations by winning a European Tour event last year.