First Test, Perth (day two, close):
Australia 375 v South Africa 243-8
Dates: 17-21 December Start time: 0230 GMT
Coverage: Scorecard and reports on BBC Sport website. Live on Sky Sports
Johnson's figures were his best so far in Test cricket
Inspired bowling by left-arm paceman Mitchell Johnson put Australia on top on day two of the first Test against South Africa in Perth.
The 27-year-old took 7-42, his best figures in Tests, as the tourists stumbled from 234-3 to 243-8 at stumps.
Jacques Kallis and AB de Villiers both made 63 in a stand of 124 but Johnson then picked up five wickets in four overs to leave South Africa reeling.
Australia were all out for 375 earlier in the day, Makhaya Ntini taking 4-72.
The home side managed to add 34 to their overnight 341-9 before Ntini had last man Peter Siddle caught behind for 23, leaving Jason Krejza unbeaten on 30.
Australia's total was a good effort, having been 15-3 on the opening morning, and South Africa needed a positive response against an attack which, in Siddle and Krejza, had two players appearing in only their second Test.
But Johnson had other ideas, having been entrusted with the new ball in the absence of injured Stuart Clark, and he soon removed Neil McKenzie for two when a poor shot saw the opener caught by Krejza.
South Africa shrugged off the setback and skipper Graeme Smith set about laying a solid foundation to their innings in tandem with Hashim Amla.
The pair added 90 for the second wicket before off-spinner Krejza produced a flighted delivery which deceived Amla and spun back to bowl him for 47 as he attempted to drive.
Australia made it a double breakthrough in the next over when Smith played on to a ball from Johnson and departed for 48.
Once again, the tourists had to rebuild but Kallis and de Villiers were equal to the task and batted together for 38 overs either side of the tea interval.
Krejza proved expensive, conceding 102 from his 25 overs, and home skipper Ricky Ponting eventually turned again to Johnson.
It proved the right decision as his devastating burst ripped through South Africa's batting line-up.
De Villiers and Kallis edged angled deliveries to keeper Brad Haddin, who claimed his third catch when JP Duminy gloved a bouncer.
They they were followed back to the pavilion by Morne Morkel and Paul Harris, who were both caught by Krejza in the space of four deliveries.
Mark Boucher and Dale Steyn survived the final over of the day, bowled by Krejza, but South Africa were 132 behind at the close and facing an uphill task to repair the damage.
"Johnson bowled a superb spell at us, [he got] a little bit of reverse swing, put the ball in the right areas and he found the edges," Kallis commented.
"Batters have got in and no-one has really gone on and got a big one which shows there is a little bit in the wicket, so that's encouraging for our bowlers as well.
"We've got to try and get as close as we can to the Aussie score and once we've done that we've obviously got to try and restrict them to as little as possible."
The world's three leading news agencies are not covering the series due to a dispute with Cricket Australia.
Reuters, Agence France-Presse and Associated Press have suspended all coverage of the 2008-09 season.
Their photographers and reporters did not supply material from within the ground. As a result, we cannot use pictures from the current match.