Thomas Aiken and Oliver Fisher took over at the top of the Africa Open leaderboard as overnight leader Emiliano Grillo endured a difficult start to throw the contest wide open.
Grillo held a two-shot lead thanks to a brilliant 62 on Saturday, but ran up a quintuple-bogey nine on the first hole at East London Golf Club.
The 21-year-old Argentinian had already taken a penalty drop from an unplayable lie when he chipped his fourth shot into a greenside bunker, from where he needed two attempts to escape.
His sixth shot then rolled back off the green and after chipping up to seven feet, he needed two putts to complete an extraordinary opening hole.
Having dropped just one shot in the previous 54 holes, Grillo suddenly found himself three off the lead shared by England’s Fisher and home favourite Aiken.
Aiken holed from 15 feet for an eagle on the third, with compatriot Ulrich van den Berg also making an eagle on the third and birdie on the fourth to lie one behind alongside compatriot Darren Fichardt and American John Hahn.
Fisher bogeyed the first after missing the green with his approach, but birdied the long third and hit his approach to eight feet at the next to join Aiken on 19 under.
Fisher birdied the sixth after a fine approach to five feet, as Aiken saved par on the eighth from a greenside bunker to remain in a share of the lead, one ahead of Hahn and defending champion Fichardt.
After a long lull in proceedings, it was all change at the top of the leaderboard when Fisher bogeyed the 13th after missing the green with his approach and Aiken dropped a shot on the 14th after finding a fairway bunker off the tee.
A birdie on the par five 15th therefore took Hahn into the outright lead on 19 under par, with Fisher, Aiken, Fichardt, Jaco van Zyl and England's David Horsey all 18 under.
Horsey had looked out of contention after a bogey on the first left him eight off the pace, but picked up shots on the fourth, sixth, eighth, 13th, 15th and 17th, the latter coming from long range across the green.