The 24-year-old from South Africa leads by two strokes over Roger Wessels, who carded an even-par 72 to land on 8-under for the tournament. Three back are Mark McNulty and last week's runner-up in the Alfred Dunhill Championship, Justin Rose.
Of the four top players, only Rose has gotten progressively better with each passing round, shooting a day-low 68 on Saturday. It follows up scores of 72 and 69.
His round might not have been so low, had it not been for a furious display of golf over the back nine of the East London Golf Club. After going out in 1-over 37, the 20-year-old from England stormed home in just 31 strokes, chipping in for eagle at the par-5 11th and following it up with birdies at holes 12, 13 and 15.
'I played well all the way around but holed nothing going out and just about everything coming back,' he said. 'After nine holes I didn't think I had a chance.'
It wasn't long ago that Rose didn't think he had a chance in golf at all. After recording a fourth-place finish in the 1998 British Open as a 17-year-old, he would go on to play dismal golf as a professional, missing 21 consecutive cuts at one point.
However, recent work with David Leadbetter and the runner-up finish last week to Australian Adam Scott has seemed to renew the confidence in his game. He appears to be coming into his own, and it was very apparent on Saturday.
'It's nice to be in contention again,' he said. 'I was aware that it could be difficult to focus after last week, but I tried to make sure I forgot about it, but used the positives in the right way.'
Otto is also trying to focus on the positives which arose from a recent and highly-publicized incident at the South African Masters, in which he snapped all the clubs in his bag and tossed them into a river following a score of 80.
He has since been remorseful for his actions and has claimed to have learned a valuable lesson.
His round on Saturday could very well have been deep into the 60s as well, as he carded five birdies on the day. But the 24-year-old grinded at times also, and offset those red figures with bogies at holes 2, 9, 12 and 18. Nevertheless, he remains confident and content at where he stands on the leaderboard.
'As for the others, they are chasing me,' he commented. 'They have to shoot 69 and me 72 to be in a playoff, and every day I feel more comfortable with my swing.'
His swing may be feeling better, but his scores are not showing it. While Rose has improved every day, Otto has worsened, going 65-70-71.
Sunday should prove extremely interesting to see how these two very young and very good golfers respond to their respective situations.
Click here for Full-Field scores from the South African Open!