He trailed a group of three players who head the field at 10-under 136 for the tournament – South African Branden Grace (69), England’s Miles Tunnicliff (69), and Austria’s Markus Brier (66).
Joining Oosthuizen one shot off the pace were South African countryman Jaco van Zyl and England’s Ross McGowan at East London.
Van Zyl, a winner of four Sunshine Tour titles last year, produced a 70, while McGowan fired a 69.
Defending champion Charl Schwartzel called his 70 “one of my better 3-unders” and was three behind the leaders, but 2009 champ Retief Goosen missed the cut by two strokes after his second-round par 73.
Oosthuizen, who rose 21 spots on the leaderboard, looked forward to the weekend with relish.
“Hopefully the wind will keep blowing because I think it’s the way this golf course should be played,” he said.
In the opening event of the 2011 Sunshine Tour, co-sanctioned by the European Tour, Oosthuizen looked in complete control in the wind.
“There was a lot of shot-making, which I like,” he said. “Like from 100 meters out, you take a 7-iron, or something like that. I still think there were quite a few birdies out there today.”
He demonstrated that after opening with an eagle-3 on the 507-yard first hole by making five more birdies on a day when all around him were dropping shots. His solitary bogey came on the 17th.
The three leaders made nine bogeys between them; two for Grace, three for Brier and four for Tunnicliff.
All of them professed to having a preference to playing in the wind.
“The two tournaments which I have won on the European Tour have been in really windy conditions, so it obviously suits me,” Tunnicliff said.
He made a superb start with five birdies on the first five holes.
“I wasn’t quite expecting that,” Tunnicliff said. “I hit some really good shots and rolled the ball in nicely.”
It came undone a little with two bogeys before the turn and two more on Nos. 15 and 16, but he chipped in on the 18th to put himself into a share of the lead.
Brier made eight birdies and an eagle in his round.
Grace was runner-up to Goosen in 2009 but won his maiden title on the Sunshine Tour in November, and his confidence was high.
“The wind is not the problem,” he said. “It’s just when it gusts that you struggle to get the balance and the stance right.”