SUN CITY, December 7, 2013 (AFP) - The 38-year-old Welshman was two clear at the halfway stage and he then grabbed birdies at the fourth and fifth holes of his third round to move four ahead.
The two-time European Tour winner did well to save par at the long ninth after hitting his approach in the water, and a birdie at the par five next took him to 14 under par for the week.
He eased further ahead with birdies at the 11th, 14th and 15th and, despite a bogey on the penultimate hole, will start the final round on 16 under, three strokes ahead of the chasing pack.
"To win here, against such a high quality field would be up there," said Donaldson. "I've won twice on The European Tour so far, and while every win is special, this would just be a little more special.
"This is a really difficult field, it's one of the best fields in the world so a three shot lead against these guys doesn't really mean much. You've got to go out there and play really good golf - that's what I'll be aiming to do tomorrow."
Donaldson's efforts meant even a fine 66 from Thomas Bjorn was not enough for the Dane to significantly close the gap.
Having managed three birdies on the front nine, Bjorn sparked into life with an eagle at ten and birdie at 11, thanks to superb approach work.
A six at 14 set him back, but the veteran picked up a shot on the last to stay alongside America's Ryan Moore.
"It is going to be one of those days when you have to go out there and try to shoot 66 or 67 and then see what Jamie does," said the Dane.
"This is not a golf course where you can go out early and chase him down because it can get away from you so quickly if you do that."
Moore, a recent winner on the US PGA Tour, turned in a three under par 33 before picking up two further shots on the back to complete a 67.
Further back on 11 under were Thongchai Jaidee, Sergio Garcia and Henrik Stenson.
Race To Dubai winner Stenson, who hit a solid 69, will wonder what might have been having twice found the water en route to a double bogey at nine.
Garcia, though, will have very differing emotions having produced one of the shots of the day to chip in at 14, his eagle followed by birdies at 16 and 17.
There was no such drama for Thongchai, who did not drop a shot en route to a wonderful 66.
Collated third round scores and totals on Saturday in the European & Sunshine Tour Nedbank Golf Challenge at the Gary Player CC, Sun City, South Africa
(Gbr & Irl unless stated, par 72):
200 - Jamie Donaldson 67-66-67
203 - Thomas Bjorn (DEN) 67-70-66, Ryan Moore (USA) 71-65-67
205 - Sergio Garcia (ESP) 66-73-66, Henrik Stenson (SWE) 69-67-69, Thongchai Jaidee (THA) 69-70-66
207 - Brendon De Jonge 70-68-69
208 - D.A. Points (USA) 71-67-70, Darren Fichardt (RSA) 71-68-69
209 - Peter Uihlein (USA) 70-69-70, Charl Schwartzel (RSA) 68-70-71, Justin Rose 73-67-69
210 - Louis Oosthuizen (RSA) 74-69-67
211 - Martin Kaymer (GER) 71-66-74, Gonzalo Fdez-Castano (ESP) 67-72-72
213 - Luke Donald 68-71-74
215 - Francesco Molinari (ITA) 76-70-69, Branden Grace (RSA) 75-71-69, Morten Orum Madsen (DEN) 76-71-68
216 - Victor Dubuisson (FRA) 73-72-71
217 - Joost Luiten (NED) 74-68-75, Thaworn Wiratchant (THA) 71-76-70, Richard Sterne (RSA) 73-73-71
218 - Matteo Manassero (ITA) 72-74-72
219 - David Lynn 73-71-75
222 - Dawie Van Der Walt (RSA) 77-72-73, Gary Woodland (USA) 74-73-75
223 - Ernie Els (RSA) 75-71-77, Peter Senior (AUS) 80-68-75, Kevin Streelman (USA) 75-71-77