Former schoolmates Ryan Rickelton and Wiaan Mulder hit centuries and swung the series-deciding third Test in South Africa's favour at Newlands on Friday.
Rickelton made 101 and Mulder 115 before South Africa were bowled out for 387 in the last over of the fourth day, setting Australia a target of 288 runs to win on the final day.
The series between the two leading Test nations is tied at 1-1.
Rickelton and Mulder both attended the elite St Stithians College, north of Johannesburg.
"It was really special," said Rickelton. "We have played a lot of cricket coming through the teenage years together and we know each other's games really well."
South Africa started the day on 140 for four -- but with a 100-run first innings deficit it was effectively a precarious 40 for four.
Matthew Breetzke (43) helped Rickelton absorb the early pressure before Mulder joined him in a sixth-wicket stand of 154.
"It was about spending time at the wicket and not getting too far ahead of ourselves," said Rickelton. "We knew that the longer we batted the more frustrated the Australians would get."
Rickelton said South Africa would be pushing hard for victory on Saturday.
"For them (Australia) to bat out three sessions will be a big ask but we will also have our work cut out," he added.
Only one wicket fell in the first five hours of the day, most of which was taken up by Rickelton and Mulder.
Just when it seemed South Africa were forging an impregnable position, Rickelton was run out shortly before the afternoon drinks break.
His dismissal sparked a collapse in which four wickets fell for 16 runs in another twist in a series which has featured numerous changes of fortune.
But Kagiso Rabada -- another St Stithians old boy -- stayed with Mulder, who reached his century during a last-wicket stand of 36.
"It was a really important partnership," said Rickelton. "Those last 20 or 30 runs will hopefully take us over the edge tomorrow."
Australian bowling coach James Franklin said the pitch had not deteriorated markedly, especially for fast bowlers, although there was some turn for the spinners.
"It's set up for a great last day of the series," said Franklin.