Faf du Plessis battled his way to his eighth Test hundred as the Proteas relentlessly batted on to 344-6 at tea of day four at the Wanderers, a lead of 611.
The decision to bat on to such formidable heights before declaring at the break was shaped by the fact that the Proteas have concerns about the fitness of their bowlers. Morne Morkel has a side strain, and at a point when the Proteas had more than enough runs, came the news that Kagiso Rabada was struggling with a sore back and Vernon Philander had a minor groin strain.
All the bowlers will have to be carefully managed.
The century was a momentous occasion for Du Plessis, who had struggled for runs throughout this series — with his best being just 20. He did this one the hard way though, batting on after receiving a tremendous blow on his finger from Pat Cummins, when he was on 43.
Ignoring the fact he had to do some strong batting, he soldiered on with even more extra padding on his glove; in fact, from that point, his stroke play became more positive and he drove with intent. His first 50 came up off 103 balls, with nine fours, the second off 63 balls, with eight fours and a six.
Du Plessis eventually went for 120 when a precise delivery from Cummins bounced more than expected to take the edge and carry to the slips, although it took an athletic dive by Peter Handscomb to complete the catch.
Dean Elgar was not far behind, but he was 19 short of his 12th Test hundred when Nathan Lyon was finally rewarded after his delivery was top-edged off a sweep. Elgar’s 81 — as befitting such a solid opener — came off 250 balls, with 10 fours and a six.
At 266-5, the Proteas had a lead of 534, but Du Plessis, it seemed, was forced to grind it out.
Philander was at least batting with freedom, scoring 33 off 49 balls, while Temba Bavuma was with him on 35 off 40. They had put on 71 in 14 overs after Quinton de Kock was trapped lbw by Cummins on four.
They have a 2-1 lead in the series and that is all they need to record their first series win post-isolation.
South Africa (1st innings) 488: Aiden Markram 152, Temba Bavuma 95, AB de Villiers 69; Pat Cummins 5-83, Nasthan Lyon 3-182
Australia 221 (1st innings): Tim Paine 62, Usman Khawaja 53, Pat Cummins 50, Vernon Philander 3-30, Kagiso Rabada 3-53, Keshav Maharaj 3-92.
South Africa (2nd innings) 344-6: Faf du Plessis 120, Dean Elgar 81, Pat Cummins 4-58, Nathan Lyon 2-116.
South Africa lead by 611.
Photo: Muzi Ntombela/BackpagePix