The Blitzboks will play Australia in the Cup quarter-finals of the Wellington Sevens following a 19-5 loss to England.
In their first two games on Friday, Neil Powell's men beat Wales 26-0 and Portugal 27-5.
Tries from Justin Geduld and Sampie Mastriet (two) gave them a 19-0 half-time lead against Wales, and Chris Dry went over in a much tighter second half to seal the win.
Kyle Brown, Frankie Horne, Chris Dry and Jamba Ulengo (two) crossed the line against Portugal.
The Blitzboks then came up against England, who scored two tries in the first half through Tom Mitchell and James Rodwell to take a 12-0 lead. South Africa hit back through a second half try from Cecil Afrika, but another Mitchell score sealed the win for England.
Meanwhile, New Zealand, who are second on the World Series standings behind South Africa, crashed to a 12-7 loss to Fiji before thrashing Spain 55-0 and France 47-0.
Cup quarter finals (Saturday):
Fiji vs Argentina
Australia vs South Africa
England vs Samoa
Canada vs New Zealand
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