Australia's lead remained large, but had a considerable amount lopped off by a defiant century from South African captain Graeme Smith on day two of the second Test at the Adelaide Oval on Friday.

Australia's lead remained large, but had a considerable amount lopped off by a defiant century from South African skipper Graeme Smith on day two of the second Test at the Adelaide Oval on Friday.

South Africa did well to drag themselves back into the contest, snaring five wickets in the session before lunch, later ensuring their effort with the bat at least matched a third of the opposition's first total.

Resuming on 482 for five, Australia boasted high hopes of a 600-plus total, instead slipping to 550 all out, with Proteas seamer Morne Morkel cherishing a five-for in trying circumstances.

The tourists replied with 217 for two, losing the precious services of opener Alviro Petersen and the in-form Hashim Amla, but riding on the back of Smith's belligerent success.

Smith's vigil epitomised a captain's knock, and enjoyed its fair share of luck en route to an unbeaten 111, after Australian wicketkeeper Matthew Wade missed a relatively straightforward chance when the left-hander was on 46.

Battling cramp amid the sapping Adelaide heat, the veteran welcomed the 26th century of his formidable Test career, and third century against the Australians. Accruing a dozen boundaries across a fighting 220 deliveries, Smith's effort would have read a lot shorter had he not won a review shortly before the final drinks break.

On 78 at the time, the opener drove at fast bowler James Pattinson's tight line and length, perhaps tickling a faint edge to Wade. With the appeal lodged and initial evidence enough, umpire Billy Bowden duly raised his finger.

A referral, though, soon begged to differ. HotSpot failed to marry ball to bat, and Snicko flat-lined throughout, with Bowden's choice overturned - and Pattinson and company collectively peeved by third official Asad Rauf's decision.

The promoted Jacques Rudolph, meanwhile, moved to a promising 25 not out after he was sent to the crease ahead of the injured Jacques Kallis and weary wicketkeeper-batsman AB de Villiers.

Sharing an unbroken 48-run stand with his captain, Rudolph was dogged in the face of everything Australia's eight-man attack had to throw at him, which included the part-time leg-spin of David Warner and freelance trundle of Rob Quiney.

The expansion of the home side's bowling ranks bore some fruit, with Warner and Wade combining to have Amla stumped for 11. This after Petersen had run himself out at the non-striker's end, near colliding with Smith before losing the race to fielder Michael Hussey's direct-hit from mid-on.

Petersen, primed to convert his 54 into three-figure proportions, will be livid for his presumption. Casually thinking the ball was headed to Smith's end, the batsman failed to ground his bat on the slide - and duly paid the price.

The morning session had belonged almost entirely to the Proteas, whose quintet of breakthroughs stifled Australia's ambition to bat just once in this match. Morkel shone, in the absence of the crocked Kallis and amid the expense of leg-spinner Imran Tahir and seamer Rory Kleinveldt.

Fetching the sixth five-wicket haul of his Test career, the lanky right-armer ended the prolific Michael Clarke's double-century on 230, castling the Australian skipper with a peachy length.

Wade came and went and tail-ender Peter Siddle obliged Kleinveldt with a consolation, maiden Test wicket, while number nine Pattinson's quickfire 42-run cameo was ended by fast bowler Dale Steyn.

South Africa, near gunned into submission by Clarke and fellow centurions Warner and Hussey on day one and still 333 runs in the red, will take heart from Friday's comeback, and the fact that they have never lost a Test in which Smith has scored a century.