Sergio Garcia was pegged back on the second day of the Nedbank Golf Challenge in South Africa.
In addition to Oosthuizen, Dylan Frittelli is also leading the South African charge as he also shot a 67 on Friday to leap to four-under-par overall, five shots behind Garcia.
Garcia, fresh from victory at the Andalucia Valderrama Masters last month, carded eight birdies as he seeks a third title at Sun City after wins in 2001 and 2003.
Four-time major victor Rory McIlroy, who needs a top-two finish to stay in with a chance of winning the Race to Dubai, is 10 shots off the pace on level par, after a one-over 73.
"I wouldn't say it was a frustrating back nine‚" said a pragmatic Garcia. It's not ideal to see three-putts, but some of the pins were nearly impossible to get to and when you leave yourself 20 or 25 feet putting over hills then it is going to happen sometimes.
He then finished well after a bogey at the eighth by following a birdie four at the 14th with a par save from 15 feet at the 16th and an impressive closing birdie from just eight feet. If you do that you can give yourself a lot of chances around here, but you need to get the ball in the fairway first.
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He leads from South Africa's Charl Schwartzel, Frenchman Mike Lorenzo-Vera and Mikko Korhonen from Finland, who all carded four-under-par rounds of 68.
New Zealand's Ryan Fox however has made a good start with a round of 69 to be 2 under and in 11th place. "I kept the ball in play all the time, which is hard to do here".
While the two-time Sun City champion put his good fortune down to the vagaries of the wind not punishing him and some "bonus putts", his round on a first visit to Sun City since 2013 was remarkable.
Ross Fisher came close to the round of the day when he made the turn in 31 after three birdies and an eagle in his first nine.
Defending champion Branden Grace is also on three under, while Rory McIlroy is eight strokes off the pace after a one-under 71.
McIlroy's front nine was promising with three birdies offset by just a single bogey, at the par-four third when his ball plugged just below the lip of a greenside bunker.
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