He leads South African rookie Nicholas Lawrence by one after Lawrence shot a 68 in the second round.
Overnight leader Bradford Vaughan of South Africa struggled mightily on Friday with a quadruple-bogey eight on the first hole after two shots found the right brush. He shot a 5-over 77 in round two and is tied for 17th at 2-under par.
The real battle this week is for the Order of Merit title and that battle is clearly being won by current leader Tim Clark, not Justin Rose, the only other player in the field who could take the crown from Clark.
Clark carded a 4-under 68 on Friday and is tied for third with Michael Green and Nic Henning at 7-under-par.
Rose, the winner of last week's South African Masters, shot a 2-over 74 and is six behind Clark as the duo began the second round tied with matching 69s.
The winner of the South African tour's Order of Merit title earns an invitation to the British Open, the World Golf Championships American Express Championship and the World Golf Championships NEC Invitational.
Bruce Vaughan's round started with an eagle at the par-5 second after a 3-wood landed 25 feet from the hole. He dropped a shot a the fourth but he rebounded with four birdies over the rest of his round with all of the birdies from inside 20 feet.
'You've got to pay attention to what you're doing here,' said Bruce Vaughan, who finds himself in the hunt for his first victory on the Sunshine Tour since 1994. 'This is a long course. Add to that the fact that the greens are really hard and most of the pins are put on slopes, and you have a layout which gets your attention.'
Lawrence opened with four birdies over his first seven holes but he dropped three consecutive strokes around the turn. He closed with three birdies in his last four holes for sole possession of second at minus-eight.
Andrew McLardy and Doug McGuigan share sixth at 6-under 138, followed by Mark McNulty, Hennie Otto and Sean Pappas, who share eighth place at 5-under.
Full-field scores from the South African Tour Championship