Debutant Faf du Plessis batted throughout the final day for a defiant unbeaten century to guide South Africa to a thrilling draw against Australia in the second Adelaide Test on Monday.

Man-of-the-match du Plessis occupied the crease for almost eight hours in a feat of physical and mental endurance to ensure the Proteas avoided defeat and take the three-Test series to a decider starting in Perth on Friday.

Australia must win the series to take the world number one ranking from South Africa.

"We tried everything in our power. We had a red hot crack. It was unfortunate we didn't get over the line," Australia skipper Michael Clarke said.

"But we didn't lose the Test so we can take a lot of positives out of that. We have to make sure physically we are as well prepared as we can for a crucial Test in Perth."

In a gripping finish, lion-hearted fast bowler Peter Siddle had Dale Steyn caught at mid-wicket for a duck and then bowled Rory Kleinveldt (3) with a yorker.

Siddle gave everything in the final over of the Test in search of the last two wickets but Morne Morkel held on.

It was the second time the South Africans had batted out for a draw in the series after denying Australia's unlikely victory push in the Brisbane opener earlier this month.

"It's (the draw) really a strengthening point for us considering we haven't played very well," South Africa skipper Graeme Smith said.

"We had another couple of big injuries in this Test match that created a hassle for us and we still managed to scrap through after not being in great positions."

Du Plessis, who needed treatment for cramp late in the day, finished unconquered on 110 with Morkel not out on eight in South Africa's 248 for eight.

"I just tried to keep my game plan very simple. Make them bowl at me and just take it an hour by an hour," he said.

"If you looked at it yesterday, it was quite a long way away. AB (de Villiers) and Jacques (Kallis) really helped me a lot. They kept me calm, especially in the 90s."

Du Plessis, who scored 78 in the first innings, was at the crease for 464 minutes and faced 376 balls in his draining knock.

He was dropped on 94 on the penultimate ball before tea when wicketkeeper Matthew Wade failed to hold onto a tough chance while standing up to the stumps to paceman Hilfenhouse.

He also survived two reviews after being given out by umpire Billy Bowden.

The first was when he was on 33 when he padded up without offering a shot to Michael Clarke's spin. The review found the ball pitched just outside the line.

Du Plessis was given out again after an lbw appeal by Clarke on 37, but another review showed there was no contact with the pad and the debutant batted on.

The allrounder's joy at reaching his milestone was tempered by the loss of the injury-restricted Kallis five balls later.

Kallis was caught off bat and pad at short leg by Ed Cowan from Nathan Lyon for 46 to end a gritty 99-run stand in 149 minutes with du Plessis.

The champion allrounder played an invaluable knock even though restricted in his mobility by a hamstring injury.

The Proteas lost the wicket of AB de Villiers shortly after lunch when he was bowled by Peter Siddle for 33 with one that nipped back to clip off-stump.

De Villiers faced 220 balls in his stoic boundary-less knock in a study of concentration, putting on 89 runs for the fifth wicket with du Plessis in 68 overs.

The Proteas gave no thought to chasing down a huge and unlikely victory target of 430, scoring just 135 runs on the final day off 67 overs up to tea.

The most successful fourth-innings run chase at the Adelaide Oval stands at the 315-6 Australia scored 110 years ago to overhaul England. The record overall winning chase is 418 by the West Indies against Australia in 2003.