Jondo then hit Lion for two sixes. Cummins messed up the stumps of this batsman who scored 39 runs in a great yorker. Kyle Verena was his victim a little later in this brilliant spell. He was caught at slip for 19 runs.
Marco Jansen (10*) and Simon Harmer (6*) spent the rest of the day.
3 wickets for Cummins, 2 for Helgewood for equal 29 runs.
Australia has already clinched the series by winning the first two Tests. Challenge to avoid whitewash faces South Africa in final days.
Australia 1st Innings: Decline 475/4 in 131 overs.
South Africa 1st Innings: 149/6 in 59 overs (Elgar 15, Eruya 18, Klassen 2, Bavuma 35, Jondo 39, Verena 19, Jansen 10*, Harmer 6*; Hazelwood 12-3-29-2, Cummins 14-5-29-3, Lion 25-8-65-1, Agar 7-1-19-0, Head 1-0-6-0