Melbourne: South Africa are in desperate trouble at 7-198 at stumps on day two of the second Test against Australia after young quick Peter Siddle grabbed three vital wickets.
Replying to Australia's first innings of 394 at the MCG, South Africa's 1-0 lead in the three-match series is now under threat.
The Proteas trail by 196 runs on the first innings with second-Test batsman JP Duminy 34 not out and Paul Harris on eight.
Home-town hero Siddle (3-24 from 13 overs) and spinner Nathan Hauritz (2-49 off 20), both playing in their third Tests and yet to establish regular places in the team, outshone pace spearhead Brett Lee (0-68).
Left-armer Mitchell Johnson continued his good form with 2-53.
Siddle dismissed Neil McKenzie (0) and AB De Villiers (7) cheaply and also took the prize wicket of skipper Graeme Smith for 62.
The 24-year-old Siddle had the crowd roaring after crashing into McKenzie's off stump in the second over.
Johnson replaced Lee in the ninth over and the West Australian struck with his third ball, claiming Hashim Amla (19) caught at gully.
South Africa's anchor man Jacques Kallis was on 26 when he fell caught behind off the bowling of Hauritz on the last ball before tea at 3-102.
Siddle broke through in the first over of his second spell when Smith, who is carrying an elbow injury, was caught behind.
In the third over of Siddle's spell, the former junior woodchopper had his third victim when De Villiers lost his off stump.
Hauritz picked up another important wicket when he had Mark Boucher (3) caught at square leg as South Africa lost 4-39 to be 6-141.
Johnson showed the gap between himself and Lee by replacing the right-armer late in the day and bowling Morne Morkel for 21 with the first ball of his spell.
Australia's tail wagged vigorously on day two, despite pace ace Dale Steyn's 5-87.
Resuming on 6-280, Michael Clarke advanced from 36 to an unbeaten 88 before Siddle fell for 19.
The pair added 42 for the 10th wicket.
Lee and Clarke contributed 45 for the seventh wicket before Steyn removed Lee (21) and Mitchell Johnson (0) within four balls.
The South African speedster's next breakthrough came in unusual fashion when Hauritz (12) was taken low down at first slip by Smith at 9-352.
Smith gestured for a video replay. Players are forbidden to call for replays, although Smith is unlikely to be fined.
Umpires Aleem Dar and Billy Doctrove instructed TV umpire Bruce Oxenford to give a verdict and the Australian official eventually gave the batsman out.