South Africa have lost five wickets for just 56 runs in the opening session on day three of the second Test.
Peter Siddle has led the charge for Australia, leaving South Africa needing a further 74 runs to avoid the follow-on.
Siddle made the breakthrough early on when he dismissed Graeme Smith, who only managed to add 11 to his overnight score of 111. Smith called for a review but hot spot supported the decision of umpire Billy Bowden.
AB de Villiers was next to go, taken out lbw with just a single run to his name by a superb Siddle delivery.
Dale Steyn and Rory Kleinveldt fared little better for the visitors thanks a strong spell from Ben Hilfenhaus, who managed to take out Kleinveldt for a duck.
A middle-order collapse forced South Africa to send the injured Jacques Kallis to the crease.
Although clearly in pain Kallis has laid the foundations for a partnership with Faf du Plessis, who is 26 not out on his Test debut.
