PERTH (Reuters) - Australia ripped through South Africa's top order in the first hour and broke two key partnerships in the second session to leave the tourists on 175 for seven at tea on the opening day of the first test on Thursday.
Vernon Philander departed when he dragged the ball onto his stumps for 10 to bring up the interval and give Mitchell Starc his third wicket of the day.
Quinton de Kock was left at the crease having hit seven fours in his 53 not out with left-arm spinner Keshav Maharaj set to join him at the start of the final session.
The Proteas, who won the toss and elected to bat, had been reeling at 32-4 after their top four batsmen went cheaply but skipper Faf du Plessis and Temba Bavuma steadied the innings with a partnership of 49.
Du Plessis was sent back for 37 in the second over after lunch but Bavuma put together another partnership of 71 with De Kock before he was brilliantly caught by Shaun Marsh off Nathan Lyon for 51, two balls after reaching his half century.
The opening morning belonged to the Australian bowlers, however, who laid to rest concerns about the fitness of two thirds of their pace attack and the WACA wicket with a rip-snorting start to the Australian cricketing summer.
Mitchell Starc, who had tested his recovery from a nasty gash on his leg with just one Sheffield Shield outing, set the tone with a opening delivery that clocked 147 km per hour and showed the WACA pitch had plenty of bounce and pace.
Four balls later and opener Stephen Cook got a thick outside edge to a Starc delivery that Mitchell Marsh soared to snatch out of the air.
Like Cook, Hashim Amla also departed caught off an outside edge without a run to his name three overs later, Josh Hazlewood claiming the first of his two wickets.
That reduced the tourists to 5-2 and it could have been worse had Usman Khawaja held on to a difficult low catch at forward square leg to dismiss Dean Elgar off Starc.
Elgar did not last long before he fell to a nick behind off Hazlewood for 12, however, and seamer Peter Siddle, also on the comeback trail after a back injury, struck in similar fashion to dismiss JP Duminy for 11.
South Africa decided against going with a four-prong pace attack in the first match of the three-test series, instead opting to hand a debut to Maharaj.