Warren Abery (70), Des Terblanche (70), Neil Cheetham (71) and Oliver Whiteley (67) are knotted in second place at 5-under-par 139.
The two biggest stars, and highest finishers, after Thursday's first round struggled in Friday's afternoon tee times.
Bruce McDonald, a 23-year-old sponsor's invite from Zimbabwe, held the opening-round lead after a 6-under 66. He only managed a 4-over 76 on Friday and is part of a group tied for 18th place.
He birdied his first two holes, but bogeys at 10, 11, 12 and 14, and a double bogey at No. 15 dropped him down the leaderboard.
Ernie Els, a three-time winner who owns a house on the course, shot a 67 on Thursday, but only posted a 75 on Friday. He is one of the 10 players tied with McDonald at minus-2.
Els struggled with the driver at two of the par-5s on Leopard Creek's back nine. He put two balls in the water at the 13th en route to a double bogey, then drove out of bounds at 15 and carded another double bogey.
The No. 3 ranked player in the world failed to get up and down for par at the 16th. Els recovered with his second straight birdie at 18, but the three-time major winner is five off the lead.
Gustafsson, a 28-year-old who played primarily on the European Challenge Tour in 2004, started on the 10th hole Friday and birdied No. 11 for the second time in as many days.
He made a spectacular run around the turn with three consecutive birdies from the 17th. Gustafsson dropped a shot at the second, then knocked his approach to a foot at the third to set up birdie.
Gustafsson parred his final six holes to take the lead through two rounds. Not bad for the medalist at Q School last month and that was only after he missed his card by finishing one place outside the top-15 on the 2004 Challenge Tour money list.
'I've never led anything like this,' admitted Gustafsson. 'I've been leading on the Challenge Tour a few times and in Austria last year, but nothing like this.'
The group tied for second place took different paths to get there. Abery recorded four birdies and two bogeys for his 70, while Terblanche mixed six birdies, two bogeys and a double bogey for his 2-under-par round.
Cheetham tallied four birdies and three bogeys on Friday, while Whiteley, who matched the lowest round of the day, totaled six birdies, including three in his last four holes, and only one bogey.
South Africans David Frost (70) and Charl Schwartzel (69), Scotland's Euan Little (69) and Leif Westerberg (70) of Sweden are knotted in sixth place at 4-under-par 140.
Marcel Siem, who won the title last year, improved to a 3-under 69 and is part of a group tied for 42nd place at 1-over-par 145.
The 36-hole cut fell at 4-over-par 148 and 79 players advanced to the weekend.