Colin Montgomerie was in a group of five players one stroke back at 7-under. There are 33 players within five shots of the lead.
Oosthuizen finished one stroke off the course record. He twice had strings of three birdies and a birdie at 18 allowed him to set a personal-best score.
Fisher also was bogey-free Friday. He had three birdies on the first six holes of the front nine and was 5-under-par on the day.
Plaphol had a bogey 5 at the No. 1 hole but answered with consecutive birdies at Nos. 2 and 3. He had six consecutive pars and then birdied three of the first five holes of the back nine en route to 4-under 66.
Wilson had to overcome two bogeys but a strong back nine -- 33 despite a bogey at 14 -- pulled him into a share of the lead.