England's win has set up a semi-final against New Zealand on Saturday, while the South Africans must recover in time to face favourites and triple defending champions Australia.
Tracey Neville's team will have few fears over the identity of their future opponents after such a big win over a team that had beaten them in their previous meeting, costing them the Quad Series title in January.
Goal shooter Jo Harten finished with 30 goals from 33 attempts, her long-range effort to beat the buzzer at the end of the first quarter bringing the capacity crowd to its feet.
The need to win the game in order to avoid the Australians in the last four had been somewhat mitigated by the Diamonds' one-goal win over the New Zealanders earlier.
But Neville was clearly determined that her side should made a statement against their fellow unbeaten opponents, not least those who had denied them a second-consecutive major title.
England's strongest seven started the match, and were immediately buoyed by the re-appearance in a supporting role of Layla Guscoth, who has undergone surgery on the Achilles she injured earlier in the tournament.
Marshalled by Serena Guthrie, England immediately imposed themselves and their opponents' cause was hardly helped by the early exit of captain Bongiwe Msomi, who hobbled off injured after seven minutes.
England emerged from a strong opening quarter 19-11 in front, and Harten's accuracy continued through a second quarter in which England extended their lead to 31-20.
Starting the second half with an almost-unassailable advantage, Neville could afford to make changes and she introduced Natalie Haythornthwaite in place of Chelsea Pitman at wing attack.
There were belated signs of the South Africans stirring and the accuracy of their goal shooter Lenize Potgeiter gave them a glimmer of hope as they reduced the deficit to nine.
But strong defending from Geva Mentor stemmed the mini-revival and another long-ranger from Harten saw England pull away again to lead 43-30 at the end of the third.
With the game all but won early in the final quarter, the tireless Guthrie's work was done and she was replaced at centre by Natalie Panagarry for the final eight minutes.
Harten also made way, her finishing figures barely hinting at the impact she had made in turning a seemingly-difficult fixture into such an easy win.