Applause erupted when the next batsman appeared - but it was nightwatchman Nathan Lyon joining David Warner, meaning Ponting was saved from having to make a difficult start to what everyone hopes will be a fairytale last-test innings after a run of failures.
Steyn had Cowan caught at second slip from just the third ball of the innings, and Philander made a spot-on decision to go for a review that had Watson ruled out lbw.
At stumps, Lyon was on 7 and Warner on 12.
The late drama threatened to undo some of the brilliant work done by Australia's underdog bowlers.
Lyon (3-41) was the only survivor from the second test in Adelaide, leaving pacemen Mitchell Johnson and Mitchell Starc, debutant John Hastings and Shane Watson to play their first tests for the summer in the deciding match.
On paper, Australia looked enormously vulnerable after deciding to leave out battle-weary Peter Siddle and Ben Hilfenhaus in favour of a debutant and three bowlers who hadn't played test cricket in months.
But in Johnson's first test in more than 12 months, he rediscovered some of his best form and was unlucky not to have more than 2-54.
Lyon broke potentially troublesome partnerships in the tail, and 22-year-old Starc (2-55) recovered from an inconsistent opening spell to bowl Alviro Petersen (30) and Jacques Kallis (2) before lunch.
Watson (1-22) did his job when injected into the attack, getting Graeme Smith (16) cheaply, and Hastings (1-51) overcame a simple dropped chance off his bowling from Ed Cowan, to claim AB de Villiers (4) as his first test scalp from his next over.
Hashim Amla was the man dropped by Cowan, but it mattered little as David Warner ran out the No 3 batsman with a direct hit during Johnson's next over.
Du Plessis came to the crease at 5-67, and at one point South Africa had lost 5-14 in eight overs.
- AAP
