The tough-as-nails opener got out of jail twice yesterday to be 111 not out at stumps, piloting South Africa out of the mire to 2-217.

It was a brave comeback, but scoring at three an over there's still a mountain to climb - the Proteas 333 behind Australia's first innings of 550 that ended before lunch.

Smith is best remembered in Australia for his courageous efforts in January 2009 when he walked out to the SCG nursing a broken hand in an attempt to save a Test match late on day five.

He fell short, but lost no admiration from his opposition - Australian veteran Mike Hussey praising his "mental toughness and character" after play yesterday.

This time it's Jacques Kallis (hamstring) who is walking wounded and nervously waiting to bat.

And this series the visitors are doggedly defending their world No 1 ranking.

Morne Morkel (5-146) says Smith is the man for the job.

"The amount of passion and pride he has got for his country and the way he is leading, a lot of the people don't see what happens in the changerooms and what is happening behind the scenes," said Morkel.

"He is a fantastic leader and we have seen it again today. We needed a guy up front to be solid and he is still there not out."

David Warner (1-27) produced some unexpected heroics with the ball on day two, getting rid of Hashim Amla for 11.

But Smith, Kallis and AB de Villiers, as well as Jacques Rudolph (25 not out) mean the Australians have plenty of big names still to knock over on what is a good batting pitch.

The best evidence of that was Australia getting through eight bowlers - Ed Cowan, Ricky Ponting and keeper Matt Wade the only players not thrown the ball.

Smith made the home side rue two decisive moments.

The first was when Wade made a meal of a stumping chance with Smith yet to reach 50, and the second when DRS overturned an emphatic caught-behind appeal from firebrand James Pattinson (0-40) which was given out by umpire Richard Kettleborough.

Hot spot showed no evidence of an edge to the keeper and Smith (78 at the time) survived being dismissed by Pattinson for a third time in the series.

"Most of our boys thought they heard a noise ... but in my opinion if Graeme had hit the ball and he was given out by the umpire I think he would have walked," said Hussey.

The hope is spinner Nathan Lyon (0-53 from 24) can find more turn in the wicket today and help take the match from the visitors.

"[Today] is a huge day really," said Hussey, who managed a direct-hit run out to claim Alviro Petersen (54) and break his 138-run opening stand with Smith.

"We might see with the hot weather some more turn come out of the pitch as tomorrow wears on.

"Hopefully there will be some more up and down variable bounce as well.

"The Adelaide Test isn't often won in the first couple of days but it can be lost in the first couple of days.

"The [Proteas] are still definitely well and truly in the Test match."

 AAP