South Africans Richard Sterne and Trevor Fisher stretched their lead to five shots on Saturday, after three rounds of the 1.3 million euros ($1.737 million) Joburg Open.
They held a healthy advantage at the event being played at the Royal Johannesburg and Kensington Golf Club which is co-sanctioned by the European Tour and the local Sunshine Tour.
Playing together, each fired a third-round 68 to share first place on 196, with compatriots George Coetzee, tournament favourite Charl Schwartzel, Jaco van Zyl and Chilean Felipe Aguilar on 201, the nearest challengers.
American Peter Uihlein is alone on 202 and the group a shot further back includes South Africans Thomas Aiken and Garth Mulroy, Tommy Fleetwood of England, David Drysale of Scotland and Lorenzo Gagli of Italy.
Mulroy and Aiken posted the best third rounds -- 65 and 66 respectively over the par-72, 6942-metre east course at the north-eastern Johannesburg club -- but bridging a seven-stroke gap on the leaders is asking a lot of the pair.
The chances of the trophy staying in South Africa for a fourth consecutive year after two wins by Schwartzel and one by Branden Grace are good with seven locals among the top 12 contenders.
Sterne, runner-up to Stephen Gallacher of Scotland in the Dubai Desert Classic last weekend, had three birdies on the outward nine to make the turn one shot behind Fisher, who was four-under-par over the first nine holes.
But Fisher had an inconsistent inward nine with three birdies and three bogeys while 2008 Joburg Open champion Sterne displayed greater stability with two birdies and a solitary bogey.
"It was pretty good going out there," said Sterne as he admitted feeling the mental and physical pressure of being a title chaser for the second consecutive weekend.
"I feel quite drained at chasing first prize twice within eight days, but I would rather be at the top of the leaderboard than in the middle of the pack. My heart was pumping quite fast out there today."
Fisher admitted to back-nine nerves: "A few set in -- you try not to think about the lead, but the board is there in front of you. I was jumpy with the swing and not waiting at the top, so I hit a few bad shots.
"But I came back nicely on the second nine with a few birdies. It is all about feeling and you have got to try and feel comfortable out there on the course as much as possible."