Australia will be faced with soul-searching and tough questions over the coming days as critical selection calls loom for the series-decider against South Africa following their crushing innings defeat in Gqeberha.

The flipping of the script could not have been more dramatic from the outcome at Kingsmead to what transpired at St George's Park after Australia were made to follow-on for just the third time since 1988. That, too, after they had South Africa 97 for 5 at the end of the second day as rain wiped out significant time.

Captain Pat Cummins said the inquest would not begin immediately to allow the emotions of the defeat to subside, but Australia will be forced to confront some home truths about their batting after losing 19 wickets in two days as they prepare for a winner-takes-all contest at Newlands.

The bowling, while less of a broader concern, won't escape scrutiny, either, after they allowed South Africa to go from 110 for 6 to 425 for 9. While Josh Hazlewood's illness was a factor, South Africa were able to absorb the injury to Anrich Nortje much more effectively. They had a specialist spinner in Simon Harmer while Australia omitted Nathan Lyon in favour of an all-pace attack with Scott Boland's inclusion and, after taking 5 for 81, he also ended up outshining many of the top order with the bat.

"We were nowhere near our best across the board really," Cummins said. "Clearly need to be a lot better than that if we want to compete. I think a loss can sometimes kick yourself into gear. You can maybe paper over the cracks sometimes in a win. Whereas I think in a loss, it makes you ask questions as a player of yourself."

After Travis Head, who made 121 in the second innings, the next most balls faced by an Australia batter in the Test belonged to Boland after he survived 166 deliveries as nightwatcher in the second innings. When asked about Vernon Philander terming the first-innings display, where they collapsed to 99, as "gutless" on SEN radio, and whether it was a fair comment, Cummins said the team had to be prepared to make tough runs.

"Depends what that means really," Cummins said of Philander's remark. "I think you've got to find a way in Test cricket. It's not always going to be easy. You saw today with Trav and Scotty, sometimes it's going to be about getting through the tough spells, sticking to your method and I think we went away from that on day four. You know, a couple of loose shots, [we] could have hung around and kind of waited for the game to come to us a little bit more."

There are three players under significant pressure: the experienced Marnus Labuschagne, the recently recalled Nic Maddinson and allrounder Beau Webster. Cameron Green is expected to be available for the final Test, although won't be able to bowl, while Josh Inglis is also fit again. Cooper Connolly is the other spare batter while Sam Harper currently remains with the squad.

After scores of 0, 48, 0 and 8 since his surprise return, Maddinson may lose his place at the top of the order but given Labuschagne's 67 Tests of experience, the call around his spot shapes as the most significant.

On the fourth day of the second Test, Labuschagne reached 39 when he tried to loft Harmer down the ground into a howling gale and was caught at mid-on. It followed twin scores of 37 in Durban and the 31 he made against Bangladesh in Darwin. Labuschagne has not passed fifty in his last 14 Test innings but in this current series has faced the third-most deliveries for Australia behind Matt Renshaw and Head.

"I think the hardest thing about opening or batting three is actually getting yourself in. [The] balls are normally doing a fair bit [and] you've got fresh bowlers. He's actually doing the hard bit, he's getting to 30," Cummins said. "I think he's got to find a way to turn those into bigger scores; 30s aren't going to win you many matches.

"But it's certainly not a technique error. It's maybe a couple of decisions [when] the game demanded something a little bit different. So, again, we'll work on that in the next couple of days. It's one Test match left in the series, we've got to win this, and then there's a bit of a break before the summer."

Despite maintaining a strong win record, Cummins acknowledged that Australia's batting line-up had not been performing well enough for some time, referencing the fact they rested heavily on Matt Renshaw during the first Test, where he made 272 runs for the match and rescued them from 124 for 6 in the first innings.

"Even last week, obviously Renshaw had an amazing game but I still think we weren't at our best, particularly in the batting," he said. "Looking around the changing room at how good our batters are and the standards they all hold themselves to, I think we're probably a little bit shorter runs of where we'd like to [be]. It's [about] what do we look like at our best? We're still finding ways to win, [but] I think we make it hard for ourselves sometimes. We've got three or four days to get it right for Cape Town. There'll be lots of conversations."

However, like head coach Andrew McDonald the night before, Cummins was also keen to keep things in context. "If you said a month ago the series was going to be a one-all after two Tests with the two top teams in the world playing over here in South Africa, I think we probably would have said that's not a bad position to be in," he said. "It was only a week ago where we won convincingly. It doesn't mean we're a terrible team overnight."

As in politics, a week has proved a long time in cricket. The one ahead will be hugely significant for Australia.