South Africa hope their tortoise and hare can pull a rabbit out of their cricket hats in the third Test against Australia.

The Proteas resume on Sunday's fourth day of the day-night Test some 70 runs ahead of Australia with just four wickets remaining.

Stodgy opener Stephen Cook, the tortoise, is unbeaten on 81, and the hare, Quinton de Kock is yet to score.

The duo are South Africa's odd couple, with Cook a limited strokeplayer but tenacious and de Kock a free-spirited powerhouse.

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Together, the Proteas hope they can extend their lead to around 200 runs.

"Stephen Cook, you know what you are going to get with him - hopefully he converts, which is his track record," South Africa's batting coach Neil McKenzie said.

"And then you have got Quinton de Kock, who has been magnificent this whole tour.

"And you're just hoping that Quinny can produce the Quinton de Kock knock that everyone knows he can do, and has been doing, of late."

McKenzie said the Proteas were confident that the pair, and the rest of the batting tail, could wag enough to set Australia a challenging run chase.

"If we can get past that 180, 200 mark, take one or two early wickets - we have done it to Australia before where we have knocked them over, so that will give the South Africans a lot of confidence," McKenzie said.

"As you know, South Africans and Australians, we fight to the death. So whatever happens, it's going to be a really quality contest."