Australia had South Africa 110-6 on day three but are now facing defeat

South Africa 425-9 dec: Bavuma 179, Jansen 85; Boland 5-81

Not since the Nottingham Ashes Test in 2005, Shane Warne's spin and watching Ashley Giles' leg glance from behind a cushion, had Australia been asked to follow-on in an away Test.

It had only happened to them on one other occasion anywhere in the world in 38 years.

But by being bowled out for 99 by South Africa in their first innings of the second Test, Australia matched those lows and handed their hosts an unlikely route to winning this Test and leveling the series.

Travis Head remains on 87 not out, but this was a calamitous day for the tourists as they conceded their biggest first-innings lead since 1984, before failing for the second time in the same day's play.

At 156-4 in their second innings they are still 170 runs behind and the Proteas now look likely winners with a day to go.

"There are a number of players playing for their careers in this innings," said former Australia opener Simon Katich, Australia's highest scorer from that Trent Bridge Test 21 years ago, on SEN Radio.

If Katich's words seem strong for a side 1-0 up in the series, this South African subsidence was the latest example of an Australian batting line-up only consistent for its inconsistency.

Bowled out for 132 in the first Test of the Ashes last winter, they piled up 511 in Brisbane in the next.

They scored 567 at the end of the Ashes, but were bundled out for 198 by Bangladesh in their next Test en route to a shock defeat.

Even the highs of Matt Renshaw's 190 in the first-Test win in Durban were countered by the fact no other Australian made 50.

And after another failure, Marnus Labuschagne appears the most at risk. He will not get another chance to bat for his place before Cape Town hosts the third Test from 27 October.

After edging a drive to third slip for 14 off Anrich Nortje in the morning, he gave it away by hitting spinner Simon Harmer to long-on after tea for 39 - his third dismissal in the thirties in the series.

It was made worse by the fact he had only survived an lbw decision on review just three balls earlier.

It is now 47 innings since the 32-year-old, once the leading batter in the world, has made a Test century.

"Only he knows what was going through his mind when he tried to take Harmer down the ground, against the breeze, when Australia are trying to play for a draw," added Katich.

"How will the Australian selectors view that dismissal?

"He's been given plenty of rope over the past few years, when plenty of others haven't, but he has."

Australia head coach Andrew McDonald said he was "disappointed" with Labuschagne's dismissal.

"For me, the option is there if the ball is the right area. It is a strength of this, but in that scenario there probably are some shots that players would take back.

"He did a lot of hard work once again. I feel like I am on repeat around the amount of 30s that he has got. That has become a danger period for him.

"We had a good partnership going and were starting to claw ourselves back into the game, albeit a long way behind.

"When you do that hard work you've got to cash in and unfortunately that wasn't to be the case for Marn. We were disappointed and he will be too."

Opener Nic Maddinson is another who must simply await his fate. He was not involved in the Wednesday-morning collapse, but only because he had already edged Kagiso Rabada to slip the night before.

Opening the batting against Rabada and Marco Jansen would be feverishly difficult for a regular opener, never mind a batter more used to the middle order.

It is because of that very fact Maddinson has chased balls outside off stump in both innings, leaving the left-hander with two ducks to go with scores of eight and 48 since his surprise recall aged 34.

As he watched on, Sam Konstas, once seen as Australia's next opener, made 151 not out for New South Wales back home.

Credit must also go to left-armer Jansen, who was superb in taking 5-33 in Australia's first innings.

He was in full flow when dismissing Renshaw, Alex Carey and Beau Webster to rip out the middle order - all three were caught between wicketkeeper and gully.

Renshaw and wicketkeeper Carey have credit in the bank, but Webster, who became the day's 13th wicket when he was pinned lbw by Harmer in the final 20 minutes, will be another looking over his shoulder.

An admirable cricketer, he averages 34.13 with the bat and 28.75 with the ball in his 11 completed Tests. But he has also now gone seven innings without a 50 since the Ashes and yet to reach three figures.

McDonald said Australia know they are not the "perfect batting unit" and he could not defend some of the dismissals.

"We've had some of these moments across the journey," he said.

"The pitch didn't play too many tricks either, there was a bit of bounce.

"You do have to give some credit to the South Africans, they exposed some of our deficiencies, but there was some batter error there.

"I think we are better than that but as we sit here now, I can't defend that."

Crucially, Head remains, having been dropped on five at gully by Jansen.

It was a sharp catch as Head cut, and shelling it was the only thing the towering 6ft 8in seamer did wrong all day.

Intrigue is added by the delayed entrance to the second innings of Steve Smith.

He survived longer than anyone else in the first innings - 88 balls for 28 runs - but was given treatment for a neck issue throughout and remained in the dressing room as evening wickets fell.

McDonald said Smith will bat on Thursday, meaning South Africa still have work to do but - after the first two days were almost entirely wiped out by rain - they have a real chance to complete a famous victory and set up a series decider.

They faced all of the questions 48 hours ago. Now the doubts around Australia's XI are as loud as ever.

Jansen sparked the collapse by nicking off nightwatchman Scott Boland with his first ball of the day at the start of the second over

Four overs later he pinned Head lbw on review for 14 before Labuschagne was brilliantly caught at slip by Harmer off the bowling of Nortje for the same score

After Jansen found the edge of Renshaw and Carey in the same over, he also had Webster caught in similar fashion for his fifth Test five-wicket haul

Wiaan Mulder bowled Smith through the gate for 28 and Mitchell Starc and Australia captain Pat Cummins followed within 11 balls

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