Since 2016 SA played 12 ODI's against Australia and the results were as follows:-
SA Wins = 11
Australia win = 1
10 if the games were in SA or Australia - one was in the West Indies (Bridgetown) and one in Manchester.
The only game the Aussies won in that period against SA was in Hobart, Tasmania. They won the game by a narrow margin. The games the Proteas win was routinely by very big margins,
So why did the Proteas do so well against the Aussies in that facet of the game and why did the performances against everybody else was so putrid in the season before the WC and in the WC itself?
I believe the answer is relatively simple - up to the early part of 2018 the Proteas benefited from three great performers in AB de Villiers, Amla and Du Plessis. The problem started with the retirement pf AB from all international cricket in May 2017 and the fact that performance-wise the bottom fell out of the performances of Amla and Faf. The squad selection remained putrid with the squads in the main being made up of have-beens and never-have beens. In the WC there was only one relatively good contributor amongst the newer payers - namely Van der Dussen - the rest was poor to putrid.
So since December we played England in all formats of the game and Australia in ODI's and T20I's/ Let face facts the Proteas was putrid against England in all formats of the game. When looking at the squad selection it was evident why the bottom fell out of the team. The same happened in the T20I games against Australia. However. the ODI squad against Australia was the reason for the improvement. The selectors brought back Klaasen into the squad after he did not do well in earlier games, He was a massive success and that was of great value in the three ODI's and by a wide margin scored the most runs in the 3 ODI's.
They also brought on board Janneman Malan and Verreinne - two players who were replacing failed players of the past. In the series Malan was the second highest run scorer - even though eh scored a duck in the first ODI. Vereimne despite a failure in the second ODI did much better than the players he replaced did.
The other contributing factor was that SA Cricket was in chaos and as a result the coaching was totally neglected, With Smith as Director of Cricket and Boucher as Head Coach some players already showed vast improvement om performance as well,