Peter Siddle took three wickets to give Australia the upperhand as South Africa were reduced to 198 for seven at stumps on day two of the second Test at the MCG in Melbourne on Saturday.
Captain Graeme Smith scored a fine 62 but kept losing wickets at regular intervals with Mitchell Johnson and Nathan Hauritz also claiming two wickets each.
Earlier, Michael Clarke was left stranded on 88 as Australia posted a respectable 394 in their first innings. Dale Steyn claimed five for 87, but the Australian lower order came up with some gritty batting performances with the last two wickets putting on 68 runs.
Clarke was unlucky to miss out on a deserved century when lastman Siddle was caught by AB de Villiers off Jacques Kallis for 19.
South Africa's reply began on a sour note when Neil McKenzie was bowled by Siddle for 0 in the second over of the innings. Hashim Amla also departed cheaply when he was brilliantly caught by Andrew Symonds off Johnson for 19.
Kallis (26) added 63 runs for the third wicket with Smith before the right-hander was caught by wicketkeeper Brad Haddin off Hauritz attempting a sweep shot.
Smith hit six boundaries in his 113-ball knock before he was caught behind off Siddle followed by the wickets of AB de Villiers (7) and Mark Boucher (3). At stumps, South Africa were left with a huge mountain to climb, trailing Australia's first innings score by 196 runs.