Australia have limped through to stumps at 2-33 after they bowled out South Africa for 225 on day one of the third Test at the WACA.
Nightwatchman Nathan Lyon (seven not out) survived the final half an hour of play along with opener David Warner (12 not out).
Ed Cowan was the first man to go in the Australian innings, dismissed for a golden duck when he tentatively prodded forward to Dale Steyn and was caught at second slip by Jacques Kallis.
Watson (10) followed when he was given out lbw on review after umpire Asad Rauf turned down the initial Vernon Philander appeal.
Earlier in the day, the Proteas looked to be cruising at 1-61 approaching lunch before Mitchell Starc bowled Alviro Petersen (30) and Jacques Kallis (two) to head into the break at 3-63.
The dismissals of Hashim Amla (11), AB de Villiers (two), and debutant Dean Elgar for a 12-ball duck shortly after the break meant the Proteas had lost 5-14 and slumped to 6-75.
Last Test centurion Francois du Plessis (78 not out) led the revival with a 57-run stand with Robin Peterson (31) and then a 64-run partnership Vernon Philander (30) before he was left stranded.
Du Plessis survived a big lbw shout on 22 after Asad Rauf turned down the Australian appeal, Rauf's decision upheld on review when the replay showed the ball going over the stumps.
He faced another lbw appeal on 49 when he shouldered arms to a Starc delivery and then brought up his half-century with a glorious back-foot drive through the covers, which was promptly followed by another off the front-foot.
Lyon looked the most likely to dismiss du Plessis before tea when he beat him in flight without luck.
Du Plessis has now scored 266 runs in the series and only been dismissed once.
Graeme Smith (16) was the first South African to fall when he edged an angled delivery off Watson to Michael Clarke at first slip.
Dale Steyn was dismissed by Johnson when he played onto his stumps attempting to leave a delivery outside the off-stump and Morne Morkel holed out John Hastings at mid-on off Lyon.
Lyon finished with figures of 3-41, but it was the two key wickets to Starc just before lunch and David Warner's run out of Amla that swung the momentum in favour of Australia.
Johnson took 2-54, while debutant John Hastings (1-51) and Shane Watson (1-22) also chipped in.