McMahon steps in for Pocock
Melbourne Rebels loose forward Sean McMahon will step in at No.8 with David Pocock ruled out with a hand injury.
McMahon hasn't started in the gold jersey since the Wallabies went down to England at Sydney's Allianz Stadium in the third Test of the June series.
The 22-year-old is the sole change to the starting XV with Cheika naming an extended bench that will be confirmed after Friday's captain's run in Johannesburg.
Fellow Rebel James Hanson will get the chance to add to his 10 Tests after being named amongst the reserves.
The hooker's last Test was over a year ago against the United States of America but gets an opportunity in the absence of Tatafu Polota-Nau.
A Test debut beckons for Rebels wing Sefa Naivalu against the Springboks, capping a rapid rise for the 24-year-old, who was playing club rugby in Victoria just two years ago.
It's a return for Kane Douglas and Scott Fardy who have also been named on the bench, with Cheika yet to decide the final make-up.
Australia: 15 Israel Folau, 14 Dane Haylett-Petty, 13 Samu Kerevi, 12 Bernard Foley, 11 Reece Hodge, 10 Quade Cooper, 9 Will Genia, 8 Sean McMahon, 7 Michael Hooper, 6 Dean Mumm, 5 Adam Coleman, 4 Rob Simmons, 3 Sekope Kepu, 2 Stephen Moore (captain), 1 Scott Sio.
Replcements – from: James Hanson, James Slipper, Tom Robertson, Kane Douglas, Scott Fardy, Lopeti Timani, Nick Phipps, Tevita Kuridrani, Sefa Naivalu.
Date: Saturday, October 1
Venue: Loftus Versfeld, Pretoria
Kick-off: 17.05 (15.05 GMT; 1:05 AEST Sunday, October 2)
Referee: Wayne Barnes (England)
Assistant referees: Johnny Lacey (Ireland), George Clancy (Ireland)
TMO: Jim Yuille (Scotland)
