Johannesburg: Australia was up against it in the fourth and final test as South Africa reached 400 in its first innings at the Wanderers on Saturday.

Temba Bavuma was 61 not out, following on from a big century by Aiden Markram and a half-century from AB de Villiers. South Africa reached 400-7 at lunch on Day 2 of the series decider.

Australia, currently weighed down by the ball-tampering scandal that's left the team in crisis, was in danger of also seeing the series slip away. South Africa leads 2-1.

Bavuma, 25 not out overnight, made just one run in the first hour of play as he struggled in overcast conditions in Johannesburg.

He came through that testing spell and had hit eight fours in his half-century.

Australia did have one success in the first session, with spinner Nathan Lyon removing Quinton de Kock for 39.