The South African sevens team beat the United States 17-12 on Tuesday to top Pool C at the Olympic Games rugby event.
Selvyn Davids scored a brace of tries, while Stedman Gans also crossed the whitewash in a narrow victory for the Blitzboks.
The win was South Africa's third on the trot at this year's Games, having beaten Ireland 33-14 and Kenya 14-5 on Monday.
South Africa will now play Argentina in the quarter-finals later on Tuesday (11:30 SA time).
In the other quarter-finals, New Zealand face Canada (10:30), Great Britain tackle the United States (11:00) and Fiji will duel Australia (12:00).
Tries: Sylvyn Davids (2), Stedman Gans
Tries: Joe Schroeder, Brett Thompson
Conversion: Madison Hughes