However, the Swede pushed his tee shot into a pond on the ninth to open the door for Coetzee and the rest of the chasing pack, including 2011 Masters Tournament champion Charl Schwartzel.
Coetzee, who fired a course record 63 yesterday to haul himself into contention, looked set to make early inroads by rolling in an eagle putt off the front of the third green.
However, after Stenson claimed a birdie, the 26-year-old - who is yet to win on The European Tour - dropped shots at the next two holes to fall further back.
Both players have been rewarded for their aggressive bravado this week yet the Swede played conservatively on the sixth after finding the rough, which led to a bogey.
And the eighth looked like being a pivotal hole when Stenson’s tee shot dribbled into a bunker while the big-hitting Coetzee found the island green in two. But the Swede steered his long birdie putt close to save par while the South African could only pick up a solitary shot.
The pressure on Stenson soon told, though, after he planted an iron off the ninth tee straight into the water which saw his lead disappear.
That gave hopes to the likes of Schwartzel, Ryder Cup hero Martin Kaymer and Thomas Aiken, who were all surging towards the top.
Meanwhile, Tommy Fleetwood closed in on a place in The 2013 European Tour International Schedule.
That honour is given to the top 119 on The Race To Dubai rankings and Fleetwood, needing a top 27 finish at the Serengeti Golf & Wildlife Estate to guarantee his card for next term, positioned himself into a tie for seventh.
Earlier, reigning champion Hennie Otto broke Coetzee's course record with a 10 under par 62.