Australia needs just four wickets to wrap up the second Test against South Africa at the MCG and move on to the third and final Test in Sydney with a 1-0 series lead.

Set 366 to win, South Africa will resume on the fifth and final day at 6-99 after Australian leg-spinner Shane Warne was again the destroyer, taking 3-43 on Thursday.

South African coach Mickey Arthur said it had been a "titanic struggle" for his side to draw the first Test in Perth and then fight hard to save the second.

"That's the sign of a champion side ... just as we think we're going to land the killer blow they tend to come back. And they come back hard at us all the time," Arthur said.

"When you play under that sort of pressure like our guys have ... and to play under continual pressure for eight days, something had to give."

Ashwell Prince is not out 16 for South Africa and Shaun Pollock is on 13. Only rain can save the tourists but hot and sunny weather is predicted for play, which is due to start at 10.30am AEDT.

Andrew Symonds took 2-6 for Australia on Thursday in the best match of his six-Test career, giving him five wickets in the game so far.

The Queenslander also clubbed 72 from 54 balls at No.6, scoring his maiden half-century in a dynamite partnership of 124 runs in 66 minutes with century-maker Matthew Hayden (137).

In a bold move, South Africa has flown uncapped off-spinner Johan Botha to Australia, with consideration being given to partnering the 23-year-old with left-armer Nicky Boje on a spin-friendly SCG.

Botha had originally been selected only for the triangular one-day series, also involving Sri Lanka, which starts on January 13.

South African paceman Makhaya Ntini has been ruled out of the third Test after injuring his left knee during the MCG match.

All-rounder Justin Kemp, who missed the second Test with a shoulder complaint, is hoping to return for the match in Sydney.

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