Tea South Africa 329 & 53 for 2 (Ackerman 33*, Starc 1-15, Hazlewood 1-22) trail Australia 429 (Inglis 102, Carey 80, Renshaw 74, Harmer 4-104, Jansen 3-60) by 47 runs
Aiden Markram and David Bedingham fell in tame fashion against the new ball as South Africa's reckless batting approach in the series-deciding Test continued.
Trailing on the first innings by 100 runs, after Australia were bowled out for 429, South Africa were a shaky 53 for 2 at tea as the tourists smelled blood on a surface that is starting to play tricks.
Hoping to claw back into the match, South Africa looked to openers Markram and Marques Ackerman after they had combined for a 158-run partnership in the first innings.
Markram loomed as a key given his strong record against Australia, and he had been in good touch through the series without going on to make a really big score. But Markram made just one after hitting left-arm quick Mitchell Starc straight to mid-off in a soft dismissal.
Bedingham, fresh off a fluent half-century in the first innings, made his intent clear with a commanding cover drive off Starc that rocketed to the boundary. But for the second time in the match, Bedingham succumbed to the short delivery when he top-edged Josh Hazlewood to deep square leg. It was a particularly disappointing dismissal for South Africa after a slew of their batters threw away wickets to let slip a commanding first innings position.
The pressure told on Ackerman, who fell agonisingly short of a maiden Test century with 95 in the first innings, when he almost was run out before tea after setting off for a single that was never on but Cooper Connolly threw wide from cover.
Earlier, Australia were bowled out midway through the second session having built a vital lead although it threatened to be larger when they were 370 for 4.
Josh Inglis hit his second Test century with 102 off 135 balls and shared a fifth-wicket partnership of 185 with Alex Carey, who made 80. Both batters were dismissed by Simon Harmer, who was South Africa's most potent bowler and he finished with 104 for 4 off 37 overs.
Inglis made the most of his opportunity after replacing an injured Steven Smith, ruled out with a neck injury sustained in the second Test. Having long been on the fringes, Inglis had not played Test cricket since December and wasn't considered for selection in the opening two matches due to a finger injury.
Playing his first red-ball match since March in the Sheffield Shield, Inglis started scratchily before superbly shifting gears as his innate aggression eventually came to the fore. His knock added to the ton he made on Test debut against Sri Lanka in early 2025.
Australia started the day's play at 330 for 4 with a lead of one run as they eyed a big first innings lead. South Africa badly needed early wickets with the second new ball, but Inglis and Carey were untroubled.
Kagiso Rabada had to wait to bowl after spending some time off the field on day two due to stomach cramps. The burden fell on Marco Jansen, who was comfortably South Africa's best seamer on day two. But he couldn't get his tail up like he memorably did to remove Cameron Green and Matt Renshaw in quick succession earlier in the innings.
Jansen's struggles were evident when he bowled a beamer to Carey, who ducked safely out of the way. The bowlers were not helped by sloppy fielding with Inglis entering the nineties after Gerald Coetzee misfielded at mid-on to continue his tough return to Test cricket.
Rabada entered the attack 30 minutes into the day's play, hoping improved health might spur a better performance after going wicketless on day two. He was left frustrated after producing an edge off Carey only for Harmer to drop a catch low to his left at slip.
Harmer's woes were compounded by his finger being split open, although fortunately not on his bowling hand. Having bandaged the wound, Harmer was deployed into the attack only to be reverse-swept brilliantly by Inglis, who reached his century in style.
But Harmer finally ended the partnership by catching the outside edge of Inglis, who coincidentally fell for the same score as his only previous Test century. Harmer did his best to rally South Africa, snaring Carey with a tossed-up delivery that was well caught low down by Markram at slip.
As has been the trend in this series, wickets fell in clumps. Australia's collapse of 10 for 3 was complete when Rabada had Pat Cummins lbw for a duck in a decision that was upheld on DRS, with ball-tracking returning umpire's call.
South Africa hoped to wrap up the lower-order quickly but Starc provided resistance and supported Connolly as Australia passed 400. Coetzee, playing his first Test since November 2024, had some belated cheer after a wayward bowling effort when he nicked off Starc for 11.
Connolly farmed the strike, refusing singles as he defended well while picking up the occasional boundary. But he was left shaken after ducking into a fierce short ball from Jansen that cannoned into the helmet.
Connolly continued batting after a concussion test, but his 83-ball knock ended when he returned a catch to Jansen.