Port Elizabeth - Australia lost four wickets before lunch on Saturday on the way to 246 all out on the third day of the second test, 177 runs behind South Africa's first-innings 423.
Opener David Warner was out for South Africa's first breakthrough, edging to Graeme Smith at slip for 70 after adding five to his overnight score, and South Africa took fairly regular wickets after until a 37-run stand between Ryan Harris and Peter Siddle for the last wicket avoided the follow-on.
Despite the late resistance, South Africa still claimed a big lead as it chases a series-leveling victory at St. George's Park, with seamers Vernon Philander and the menacing Morne Morkel taking three wickets each.
After Warner, Nathan Lyon was bowled by Morkel, Brad Haddin had his middle stump knocked out by Dale Steyn and Mitchell Johnson missed a straight one from spinner JP Duminy after being roughed up by Morkel to end the first session and keep the pressure squarely on the Australians.
Steve Smith was out for 49 straight after lunch and although tailender Harris launched a big six over midwicket to avoid the follow on and cut the deficit to less than 200, he eventually edged behind to Faf du Plessis for a run-a-ball 26, giving Morkel his third wicket.
South Africa was in control but had problems of its own with bowler Wayne Parnell and batsman Hashim Amla off the field with injuries since the morning. Parnell went to the hospital for a scan on a left groin injury and Amla dislocated the ring finger on his left hand attempting a sharp catch in the gully.