Starc bagged 6-72 at Newlands on Tuesday to have South Africa all out for 329 at stumps on the opening day of a third and deciding Test that for a while looked to be all the Proteas.
On a chaotic morning, Steve Smith first ruled himself out with a neck injury to make for four Australian team changes from last week's loss, then Pat Cummins sent South Africa in on a flat wicket.
The Proteas reached 0-158 as Cummins began copping criticism for his decision, before Nathan Lyon kicked off a collapse of 5-29.
By stumps the Test was back in the balance, with Starc taking four wickets in six deliveries with the second new ball swinging prodigiously.
Starc trapped Ryan Rickelton in front for 42, bowled Marco Jansen (52) and Gerald Coetzee (0), before also getting Kagiso Rabada leg-before for a duck.
With several big moments and big series on his resume, Starc chose the right moment to stand up for Australia with the series on the line and a hero needed.
"If you can delete the first session, I think we had a pretty good day," Starc said.
"There was clearly not as much sideways movement and swing as we thought there might be on offer.
"They pounced on that in the first session.
"We had to reassess at lunch.
"At one point we were probably looking like we would be bowling a fair bit tomorrow, so to bowl them out today, a good close to the day."
Australia have a chequered history at the picturesque Newlands, including being bowled out for 47 in 2011, and the ball-tampering scandal on their last visit in 2018.
And for the first session, it looked like another grim chapter was coming.
Aiden Markram and Marques Ackerman's opening stand was the biggest against Australia after they'd elected to bowl in a Test in 56 years.
The decision looked questionable from the moment Markram (78) pulled Cummins' fifth ball of the match for six, sending it deep on to the hill over mid-wicket.
At that point the Test was only 6.5 overs old.
Lyon was brought on in the 11th over and Ackerman hit him over the long-off boundary, before the left-hander lifted Cummins over fine leg.
In all the Proteas hit 23 boundaries in the 27-over first session.
Australia's morning was summed up when Markram hit Starc straight to cover on 39, only to see Travis Head put down the simplest of catches
Starc's reaction, as he put his collar between his teeth, said it all.
But when Lyon (2-71) smartly darted a ball out wide with Ackerman keen to charge him on 95 after lunch, the left-hander fell and the tourists had a spark.
Lyon grabbed another when he bowled Temba Bavuma for a duck, and Cooper Connolly claimed his first Test wicket by getting Matthew Breetzke lbw.
Starc's hands also played a role in the collapse, taking a diving boundary catch to remove Markram when the opener skied Josh Hazlewood to backward-square leg.
And when he bounced out the hooking David Bedingham on 50 with the help of Hazlewood's smart work on the boundary and had Wiaan Mulder caught behind two balls later, Australia were back.
And while Jansen and Rickelton put on 95 for the seventh wicket after tea, Australia still have a sniff at Newlands on a day that at one stage looked destined to have them lose the series and top spot in the ICC rankings.
"If you gave us 329 before today's play we probably would have taken it," Ackerman said.
"But we would all agree we probably left a bit out there today."
Meanwhile, Smith's absence, after he briefly batted in the nets on Tuesday morning, made for Australia's most mid-series changes since after the events of Cape Town 2018.
Josh Inglis came in for the vice-captain, while Scott Boland, Nic Maddinson and Beau Webster were dropped, with Lyon, Connolly and the fit-again Cameron Green all coming in.
