AB de Villiers gave South Africa the edge as they ended on 263 for seven, a lead of 20 runs after Australia were bowled out for 243.
de Villiers counter-attacked to hit 74 not out off 81 balls to overcome a clutter of wickets either side of tea.
Earlier, Dean Elgar made 57 and Hashim Amla scored 56 as they added 88 for the 3rd wicket, blunting the reverse swing of the Australian attack in tough batting conditions.
South Africa 263 for 7 (De Villiers 74*, Elgar 57, Amla 56) lead Australia 243 by 20 runs.
Matches Tagged in ClipDex2018 RSA v AUS 2nd Test
Series Tagged in ClipDex2018 RSA v AUS Test serie ...
Players Tagged in ClipDexMarsh, Mitchell R Lyon, Nathan M Elgar, Dean de Villiers, Abraham B de Kock, Quinton Philander, Vernon D Amla, Hashim M Starc, Mitchell A
Grounds Tagged in ClipDexSt George's Park
Categories Tagged in ClipDexTest Matches