Dawid Malan and captain Jos Buttler both hit centuries as England overcame a poor start in the third ODI against the Proteas at the Diamond Oval in Kimberley on Wednesday.
Malan made 118 and Buttler 131 to enable England to pile up 346-7 after being sent in.
It was a total that seemed unlikely when Lungi Ngidi took the first three wickets to reduce the tourists to 14-3 in the sixth over.
The left-handed Malan and his right-handed captain rebuilt the innings, slowly at first and eventually in a torrent of runs.
Their partnership was eventually worth 232 off 211 balls.
South Africa, holding a winning 2-0 lead in the series, opted to go into the match without their two fastest bowlers, Anrich Nortje and Kagiso Rabada, and appeared powerless to keep the scoring in check even after the two centurions were dismissed.
Ngidi took 3-8 in a four-over opening spell but was expensive later on, finishing with 4-62. His last four overs cost 47 runs.
There were 19 sixes in the England innings, six of them by Malan, who faced 114 balls, and seven by Buttler, who faced 127 deliveries.