Magnus Carlsson, another Swede, joined Coetzee three off the pace when he picked up three shots in the last four holes.
The first fives holes after the turn have been less kind to Stenson this week and, after a bogey on the tenth, he had to wait until the 15th before he could reclaim a shot.
A bogey followed and the Swede’s lead looked like evaporating further on the 17th when his tee shot landed in the thick rough.
Yet Stenson produced his best shot of the day to land the ball within a couple of feet to record his sixth birdie of the day before he signed for a three under par 69.
Earlier in the day the big-hitting Coetzee had given himself a great chance to succeed 2011 champion and fellow South African Hennie Otto in winning his national title.
The 26-year-old, who is bidding for a maiden European Tour win, birdied exactly half of the 18 holes while he also picked up an eagle when he chipped in on the 445 yard par four fourth.
The only blemishes on an otherwise faultless round came on the 12th and 15th when his overly-aggressive putting led to bogeys. However, he recovered with a birdie-birdie finish to sign for a 63.
"I just gave it the best I could and lucky for me I got the birdies I needed," Coetzee said afterwards.
"I felt I handled my bogeys a lot better than in the past. Before I would put pressure on myself to make birdie the next hole, but I just waited for my opportunities."
The tournament's leader had not failed to notice Coetzee's record breaking round, but Stenson was pleased he was able to retain his cushion going into the final 18 holes.
He said: "I’m still in the same position even though I’ve got George and Magnus breathing down my neck. I’m still in good shape going into the last round.
"George was on fire today, so I’ll obviously need to watch out. But the final round is about focusing on your own game and playing well, and what happens happens. I’m focused on playing well in the final round and winning this championship."
Stenson’s ability to stay ahead of the pack also bodes well for his chances of making next week’s DP World Tour Championship in Dubai - where the 28 year old currently resides.
He came into this event ranked 59th with the top 60 guaranteed a place in the showpiece event.
A number of other players are also battling for their playing privileges with spots on the 2013 European Tour International Schedule at stake.
Lloyd Saltman needs to overhaul the rest of the field to jump up from 191st and move inside the top 119, yet his hopes were scuppered when he planted an approach into a live electric fence on the 11th for his second double-bogey of the day.
Tommy Fleetwood, who must move up five places to be given a playing card again next year, remains on the periphery of the top ten after shooting 71.