Matt Renshaw turned the tide with a blistering 190 at Durban, eclipsing the previous Australian mark of 160 by Phillip Hughes.
The left‑hander faced 397 balls, smashing 21 fours and a six, and nudging the team from a 84‑4 slump to a 390‑all‑out first‑innings.
A 134‑run partnership with Nathan Lyon for the ninth wicket kept the hosts on their toes, with Lyon contributing 27 off 92.
Australia’s comeback was demoralising for South Africa, who were 27‑1 at the end of day two, trailing by 363 runs.
With the record in hand, Renshaw sets the stage for a dominant chase, and Australia heads into the final match aiming for a series sweep.