Marsh, Smith put Oz in charge

They were reeling at 98 for four after being sent in to bat but Marsh (122 not out) and Steve Smith (91 not out) added an unbeaten 199 for the fifth wicket with positive stroke play.

"Shaun was amazing all day," said Smith.

"He let the ball come into his areas, left really well and capitalised when they bowled in his areas."

Smith said Australia were in a good position against the world champions.

"We thought it was going to be quite tough this morning but if we got through that initial phase it was going to be quite a nice wicket to bat on.

"It actually played well throughout the day with good pace and bounce.

"There are a few cracks forming so hopefully with the heat overhead we can get a big first innings total and let the cracks come into the game later."

It was a remarkable comeback for the left-handed Marsh, who just a week ago was contemplating a spell of domestic Sheffield Shield cricket.

Marsh, 30, was selected for the tour but had to withdraw because of a calf injury.

He made a quick recovery, however, and arrived in South Africa on Sunday after Shane Watson was ruled out of the first Test, also because of a calf injury.

It was Marsh's first Test in two years.

He made 141 and 81 in his first two Test innings in Sri Lanka in 2011 but was dropped after his next nine innings yielded only 79 runs.

Marsh started his innings when Australia were 24 for two in the ninth over. David Warner hit two boundaries off Dale Steyn in the first over of the match but made only 12 before he was bowled by Steyn, edging an attempted cut into his stumps.

Chris Rogers made four before he was caught at short leg off Morne Morkel.

The tall fast bowler's first delivery of the match, after he replaced Steyn, was a bouncer which struck Rogers on the shoulder.

The next ball was another lifter which Rogers fended to the leg side, with JP Duminy diving to his right to take a good catch.

New cap Alex Doolan and Marsh added 48 for the third wicket before Doolan was caught at midwicket off Ryan McLaren for 27.

Captain Michael Clarke became Steyn's second victim when he top-edged a hook to fine leg after scoring 23.

Marsh, who survived a sharp chance to Hashim Amla at gully off Morkel when he had 12, went through a quiet period when he scored only nine runs in 18 overs on either side of lunch but reached his half-century off 101 balls.

Batting with increasing fluency, he notched his century off 174 deliveries, with 11 fours.- 'They batted really well' -

South African captain Graeme Smith said at the toss that he wanted to put Australia under pressure at the start of the series.

The pitch was well-grassed and there was early life but conditions eased under a hot sun as the ball lost its shine and Marsh and Smith tamed South Africa's pace-based attack.

Marsh batted with discipline, resisting any risky strokes outside the off stump, and took 118 balls to reach his half-century, with seven fours.

He batted particularly impressively after South Africa took the second new ball late in the day. By the close he had faced 178 deliveries and hit 12 fours.

McLaren, whose only previous Test appearance was four years ago, said South Africa's decision to bowl was based on recent history at Centurion.

"The ball was moving around in the beginning but the wicket played slower and better as the day wore on.

"We had a real opportunity at 98 for four but they batted really well."