Their gambles in selecting the 30-year-old ahead of many better-performed rivals in the Sheffield Shield for the tour, in reinstating him to the squad with just one Twenty20 match to prove his fitness after a calf injury, and in choosing him in the team three days after he arrived in South Africa were all handsomely rewarded as his unbeaten century was pivotal in Australia reaching 4-297 on day one at Centurion Park after being sent in by South Africa captain Graeme Smith.

Besides Marsh, the other player chiefly responsible for rescuing Australia after it slumped to 4-98 soon after lunch was Steve Smith. The 24-year-old demonstrated his maturity, and talent, in sharing an unbeaten 199-run partnership with Marsh that stretched 56 overs - including eight with the second new ball.

While Smith only reached his half-century in the 70th over, two balls before Marsh reached his century, he significantly lifted his scoring rate in the last hour. This included crunching two fours off the first over of the second new ball, prompting the top-ranked Philander to be replaced after just that one over.

At stumps, Marsh was unbeaten on 122 from 232 balls, with Smith 91 not out from 178.

When West Australian Marsh nudged a single off part-time spinner J.P. Duminy to reach his milestone, the first cheers within the venue conspicuously - and vociferously - came from the Australian team balcony. Phillip Hughes, the prolific run-scorer who Marsh was chosen ahead of, was among the enthusiastic celebrators.

Marsh has not moved fluently between the wickets, perhaps a repercussion of that calf injury, but nevertheless clearly outperformed debutant Alex Doolan, who squandered an assured start to fall for 27.

For the Proteas, the wisdom of sending the visitors in was seemingly limited to the first hour, when Vernon Philander and Morne Morkel stood out for the threat they posed, the former through sideways movement and the latter through good pace and steepling bounce.

A clear sign of Marsh's resilient intent, after he was given the number-four batting berth ahead of Clarke, was that in the first 100 deliveries he faced he left a third of them.

The left-hander made the most of being spared on three occasions, although only two of those could be considered blunders by the Proteas.

For the first, when he was on 12, gully fielder Hashim Amla did well to even get his left hand to an ankle-high chance he had to dive full length to his left for. The second came on 57, when he was surprised by bounce from a Ryan McLaren delivery and the ball lobbed to cover from high on his bat, where Robin Peterson failed to take the overhead chance because he mistimed his jump.

The third came on 83 when he attempted a third run on a misfield but underestimated Dale Steyn's speed and throwing power. Had Ryan McLaren not fumbled the ball at the non-striker's stumps, Marsh would have been dismissed.

Debutant Doolan was at the crease in just the fifth over of the day after David Warner attempted to cut Dale Steyn to the boundary off the back foot but underestimated the right-armer inswing and chopped onto his stumps for 12.

His partner Chris Rogers lasted only three more overs before his attempt to smother a chest-bound delivery from the towering Morne Morkel allowed J.P. Duminy to take an excellent sprawling catch at short-leg, with the left-hander departing for four with his team 2-24. It brought together newcomers Doolan and Marsh.

Tasmanian Doolan, who had earlier been presented with his baggy-green cap by former Australia all-rounder Andrew Symonds, handled the South African bowlers, particularly the probing Philander, better than the openers did. He looked at ease at the crease until the Proteas turned to bowling all-rounder Ryan McLaren in the second half of the first session.

Doolan was twice fortunate to avoid edging McLaren behind in the 31-year-old's second over, and after two consecutive maidens turned to aggression the next time he faced him. He attempted a pull shot that, had it been better directed, would have brought up the 50 partnership between he and Marsh. Instead he picked out Alviro Petersen at mid-wicket, and continued his recent trait of producing innings that look elegant but fail to culminate in a major milestone.

His replacement, Clarke, had a nervous moment early in his innings when he was tardy in attempting to withdraw his bat to a delivery angled into him from Philander, with the resulting inside-edge avoiding his stumps.

While Steyn was accurate, his inability to train hard for much of the past month due to injury - and that he was reportedly affected by a bout of gastro - was reflected in his pace hovering around 135km/h, comfortably below his speed when firing. It was therefore little surprise that the bowler Graeme Smith turned to for a pre-lunch blast was Morkel.

Steyn was entrusted with the ball immediately after lunch and justified his recall. He was miserly and, more significantly, tempted captain Clarke into a hook shot that was top-edged and fell safely into the hands of Philander at fine-leg, to leave his team at 4-98. It proved to be not just the only wicket of the session but the entire post-lunch period.

As well as its day-one score, Australia will also be rapt that pacemen Steyn, Philander and Morkel bowled 54 overs between them in hot conditions. A key reason for this was left-arm spinner Robin Peterson's inability to restrict scoring. Australia's plan to target Peterson, to restrict the rest time for the Proteas' seamers, was disclosed last week by Warner. Until Peterson's spell before the second new ball it comprehensively worked, with Graeme Smith not turning to him for 39 overs before then.

Like nearly everything that happened on day one for Australia, Marsh and Smith were chiefly responsible for the success of that plan. And, ominously for the Proteas, they will both resume on day two.

Australia (1st Innings)

C. ROGERS c Duminy b Morkel 4

D. WARNER b Steyn 12

A. DOOLAN c Peterson b McLaren 27

S. MARSH not out 122

M. CLARKE c Philander b Steyn 23

S. SMITH not out 91

Sundries (4b, 3lb, 6w, 1nb) 14

Total (4 wkts - stumps) 297

Fall of wickets: 15 (Warner), 24 (Rogers), 72 (Doolan), 98 (Clarke)

Bowling: D. Steyn 20-4-54-2, V. Philander 16-2-55-0, M. Morkel 18-5-56-1 (w-1), R. McLaren 16-4-53-1 (nb-1, w-1), R. Peterson 10-0-34-0, JP Duminy 10-1-34-0.