The former British Boys champion looked on course to break the magical 60 barrier after posting nine birdies in the first 16 holes at Pretoria Country Club, including a run of five straight gains from the eighth, before failing to chip in from the edge of the green on the 17th and finding the bunker off the tee for a bogey at the last.
Otaegui move 11-under for the tournament, two-strokes clear of South Africa???s Merrick Bremmer who responded from back-to-back dropped shots in the middle of his four-under 66 to end strongly with four birdies from his final six holes.
Overnight joint-leader David Horsey remains in contention as part of the group a further shot back, despite having an up-and-down one-under 69 which saw the Englishman card a double-bogey at the par four fourth as well as three further bogeys.
Horsey???s tied on eight-under with last week???s Africa Open champion Trevor Fisher Jr, who reached the turn in just 31 after shooting five birdies on his front nine, with compatriot Keith Horne and Italy???s Edorardo Molinari also heading into the weekend three adrift of the clubhouse lead.??
???I gave a few silly ones away and just missed it on the wrong side occasionally, so a little disappointing I suppose,??? Horsey said. “But I still made a fair share of birdies to keep it under par.
???I???m still only three behind, so there???s a long way to go and this course can yield a lot of birdies as well as birdies, so I???m in a nice position.???
Wallie Coetsee seemed certain to pull closer to the leaders when a birdie at the 17th moved the South African within two of the lead, but a double-bogey at the last left him settling for a round of 69 and a share of seventh-place alongside fellow home favourites George Coetzee and Dean Burmester.
Denmark???s Morten Orum Madsen made a nightmare start to Friday after following up an opening round 63 with two double-bogeys from the first four holes, ending the day one clear of defending champion Ross Fisher on five-under for the tournament.
Europe???s Ryder Cup captain Darren Clarke safety made it through to the weekend with a second round 67, but on an afternoon where play was held up for nearly an hour due to the threat of lightning, the Northern Irishman slipped back to two-under with two double-bogeys from his final six holes.??
Two-time European Tour winner Andy Sullivan won???t complete a hat-trick of titles in South Africa, with the Joburg Open and South African Open champion missing the cut for a second week running despite ending with successive birdies in a one-over 71.