DURBAN (AFP) - South Africa's batting crumbled after Australian fast bowler Mitchell Johnson struck hard at their top order on a dramatic second day of the second Test at Kingsmead here on Saturday. South Africa were 138 for seven at the close in reply to Australia's first innings total of 352. Johnson took two wickets in his first over, then forced Graeme Smith to retire hurt with the third ball of his next over to throw the South African innings into disarray. Smith was unlikely to bat again after suffering a fracture at the base of the little finger on his right hand, an injury likely to keep him out of action for two to three weeks, almost certainly ruling him out of the third and final Test. In a second spell Johnson hit senior batsman Jacques Kallis on the jaw. He too retired hurt. He required three stitches under his chin. But X-rays revealed no damage and Kallis returned to bat at the fall of the fifth wicket. He was dismissed two balls later without adding to his score of 22. Johnson yorked Mark Boucher and had figures of three for 37, while medium-pacer Andrew McDonald took three for 25. JP Duminy was the only South African batsman to play with confidence, making 73 not out. South Africa's collapse came after the hosts had fought back earlier in the day, taking the last six Australian wickets for 49 runs, including the last five for four runs in 18 balls. Wickets tumbled on Saturday after rain delayed the start of play by half an hour. Australia slumped from their overnight 303 for four. It put South Africa right back into the match; but then it was their turn to collapse with their first two wickets falling for no runs in the first five balls. The left-armed Johnson had Neil McKenzie caught behind then trapped Hashim Amla leg before, with Amla making an unsuccessful referral to the television umpire. After Smith's injury, AB de Villiers made only three before he was leg before to Ben Hilfenhaus; South Africa crashed to six for three. Kallis and JP Duminy dug in with a half-century stand before Kallis was injured, with Boucher lasting only nine balls. Australian overnight batsmen Mike Hussey and Marcus North survived for almost an hour against some fiery fast bowling from Dale Steyn and Morne Morkel. Hussey battled his way to his first half-century in five Tests against South Africa this season before he had his off stump knocked out of the ground by Morkel. Hussey made 50 off 144 balls with nine fours. Hussey and North added 63 for the fifth wicket at just over two runs an over. Steyn and Morkel were rested but North (38) was caught at square leg off Kallis before Brad Haddin and Johnson were dismissed off successive deliveries by Makhaya Ntini in the next over. Steyn needed only four balls after lunch to take the last two wickets. SCOREBOARD AUSTRALIA, first innings (overnight 303-4) P. Hughes c McKenzie b Kallis 115 S. Katich c Smith b Steyn 108 R. Ponting c McKenzie b Harris 9 M. Hussey b Morkel 50 M. Clarke b Harris 3 M. North c Steyn b Ntini 38 B. Haddin c Amla b Ntini 5 A. McDonald not out 4 M. Johnson lbw b Ntini 0 P. Siddle c Boucher b Steyn 0 EXTRAS (b6, lb4, nb8, w2) 20 TOTAL (107.4 overs) 352 Falls: 1-184 (Hughes), 2-208 (Ponting), 3-269 (Katich), 4-266 (Clarke), 5-329 (Hussey), 6-348 (North), 7-348 (Haddin), 8-348 (Johnson), 9-352 (Siddle) BOWLING: Steyn 25.4-3-83-3 (2w) Ntini 19-4-58-2 Morkel 24-4-81-1 (6nb) Kallis 15-4-49-2 (1nb) Harris 21-5-66-2 (1nb) Duminy 3-1-5-0 SOUTH AFRICA, first innings N. McKenzie c Haddin b Johnson 0 G. Smith retired hurt 2 H. Amla lbw b Johnson 0 J. Kallis c Ponting b McDonald 22 A. de Villiers lbw b Hilfenhaus 3 J. Duminy not out 73 M. Boucher b Johnson 1 P. Harris b McDonald 4 M. Morkel b McDonald 2 D. Steyn not out 8 EXTRAS (b10, lb12, nb1) 23 TOTAL (7 wkts, 57 overs) 138 Falls: 1-0 (McKenzie), 2-0 (Amla), 3-6 (De Villiers), 4-62 (Boucher), 5-104 (Harris), 6-104 (Kallis), 7-106 (Morkel) BOWLING: Johnson 16-5-37-3 Hilfenhaus 11-2-28-1 (1nb) McDonald 12-4-25-3 Siddle 13-6-20-0 North 4-3-6-0 Clarke 1-1-0-0. To bat: M. Ntini. Umpires: Asad Rauf (PAK), B. Bowden (NZL). TV umpire: S. Bucknor (WIS). Match referee: J. Crowe (NZL).