Australia were in a commanding position at stumps on the third day of the third and final Test at the Sydney Cricket Ground, leading South Africa by 155 runs after dismissing the visitors for 327 late in the day.

The Proteas resumed on Monday morning on 125/1, with form batsmen Jacques Kallis and Hashim Amla at the wicket.

Kallis (37) was the first to go this morning, caught by Matthew Hayden at slip off the tireless Mitchell Johnson in the second over the morning.

Perth hero AB de Villiers was run out by virtue of a direct hit from Johnson with his score on 11, and when Amla (51) was trapped lbw by debutant Andrew McDonald — his first Test wicket — the Proteas were struggling at 166/4.

At the lunch break, the visitors reached 176/4 with JP Duminy and Mark Boucher the not out batsmen.

Matters got worse for the Proteas shortly after the lunch interval when rising star JP Duminy, a hero with the bat in Melbourne, was adjudged lbw off the bowling of Johnson for just 13. Duminy, however, was unlucky, with replays suggesting that the ball would have missed the stumps by quite a distance.

With SA's total on 193/5 (and with Graeme Smith having retired hurt on Sunday with a fracture in his hand), fast bowler Morné Morkel joined veteran wicketkeeper Mark Boucher at the wicket.

A massive stroke of luck went Boucher's way early in his innings when a delivery from off-spinner Nathan Hauritz struck his pads and rolled onto his leg stump without dislodging the bails.

Some indifferent bowling from the Australians in the hour before tea let the batsmen off the hook somewhat, as Boucher and Morkel batted out the rest of the session to reach 251/5 at the tea break.

It was more of the same after the interval, with Hauritz and new all-rounder McDonald looking particularly toothless.

Boucher and Morkel had added 115 runs for the sixth wicket when Ponting recalled Peter Siddle to the bowling line-up.

The bowling change proved an inspired decision by the under-fire Australian captain.

Siddle first beat Morkel for pace with a straight delivery and cleaned bowled the tall left-hander for 40 — his highest score in Test cricket — before another straight delivery accounted for spinner Paul Harris; trapped plumb in front for two.

Dale Steyn (six) was the next to go, as a quick Siddle delivery bowled from round the wicket beat the Proteas paceman and crashed into his leg stump.

Having already achieved his highest score against Australia, 'keeper Boucher was in danger of being stranded short of a well-deserved century and started to farm the strike more than he had done previously when Makhaya Ntini arrived at the wicket.

It worked for a short while, as Hauritz was dispatched for a straight six.

However, with his score on 89, Boucher was castled by another quick Siddle delivery and the visitors were all out for 327 — handing the Australians a valuable 118-run first innings lead on a deteriorating pitch.

Siddle was by far the best of the Australian bowlers, taking 5/59 — his final spell of 4/8 being particularly destructive.

Siddle's efficiency in dismissing the South Africa lower order meant Aussie openers Matthew Hayden and Simon Katich were left a tricky six-over period to negotiate before stumps.

The under-pressure Hayden looked positive from the get-go, smashing Steyn for two boundaries in his first over. But the South African quick should have had the last laugh when one kept low, striking Hayden on the pads right in front of the stumps. For once, luck was on Australia's side, as umpire Asoka de Silva gave the big left-hander not out.

At stumps on Day Three, Australia had reached 33 without loss, handing them a commanding 151-run lead with all ten second innings wickets still in tact.

SA — under the guidance of stand-in captain Neil McKenzie, in the absence of the injured Graeme Smith — face an uphill task to save this Test match, but, to be honest, it matters little in the greater scheme of things with the Proteas having already claimed the series victory after wins in Perth and Melbourne.

The visitors, however, will be geared up to put one over their hosts in the two Twenty20 internationals and the five ODIs that take place later this month.