Scott Jamieson carded a 4-under 68 on Saturday to secure a five-stroke lead after three rounds of the Volvo Golf Champions.
Jamieson is eyeing his second win in Durban in a little over a month after picking up his first European Tour victory at the Nelson Mandela Championship in early December.
Louis Oosthuizen entered Saturday with a one-shot lead over Jamieson and Thailand's Thongchai Jaidee, but the 2010 Open champion stumbled to a 2-over 74.
Jamieson sits at 15-under 201 through 54 holes, while Oosthuizen, first-round leader Jaidee (73) and Julien Quesne (67) are tied for second place at 10- under.
"It was another great day," said Jamieson. "I didn't play as well as I did the first two days, especially tee-to-green, but managed to score well and that's the main thing."
Padraig Harrington carded a 67 at inclement Durban Country Club to move into a tie for fifth with Francesco Molinari (68) at 8-under, while former Open champion Paul Lawrie, Shane Lowry and Danny Willett all shot 70 -- good for a seventh-place tie at minus-7.
Matteo Manassero fired a 66 -- the second-lowest round of the day behind Ricardo Santos (65) -- and resides alone in 10th at 6-under.
Defending champion Branden Grace bounced back from an opening-round 75 with scores of 67 and 69. The South African highlights a large group, which also includes current Open champion Ernie Els (71), tied for 11th at 5-under.
Grace's native land has been kind to Jamieson, who tied for third place at the Alfred Dunhill Championship in Malelane just a week after securing his first European Tour win.
Perhaps it has been the weather.
The Nelson Mandela Championship was shortened due to heavy rain and the Volvo Golf Champions has similarly been marked by downpours and blustering winds.
And the Scotsman has excelled.
On Friday, Jamieson birdied four of his first six holes en route to an 8- under 64, which matched Oosthuizen's tally for low round of the day. When the latter stumbled out of the gate on Saturday, Jamieson and Jaidee found themselves battling for the lead.
Jaidee picked up a pair of early birdies and built a three-stroke advantage entering No. 8, where the he hit an errant tee shot and settled for bogey. Jamieson then placed his approach within five feet on the same hole and rolled home the eagle putt to pull even.
"That definitely got me kick-started," Jamieson acknowledged.
On the 11th, Jamieson initiated a string of three straight birdies with a chip-in from the rough. He drained a 12-foot putt on No. 12 and capped the run with a tap-in on the 13th for a three-stroke lead over Jaidee at 15-under.
As the rain intensified, Jaidee missed a short par put on No. 16 and bogeyed again on the last.
Jamieson played his final two holes at bogey-birdie to close with a five-shot lead.
NOTES: Despite carding the low round of the day, Santos sits alone in 26th place for the tournament at 1-over ... The field includes the first two winners of the 2013 campaign, every winner from the 2012 European Tour International Schedule, past champions of the event, and golfers with 10 or more European Tour victories ... Last year, Grace birdied the first playoff to hole defeat Els and Retief Goosen.