Theo Brunner/Casey Patterson, United States (17) defeated Jamaine Naidoo/Leo Williams, South Africa (41) 2-0 (21-18, 21-12).
It was the first FIVB World Tour meeting between the two teams.
In Pool H, the United States is 2-0, advancing to the knockout phase, and South Africa is 0-2. Also in Pool H, Brazil's Gustavo "Guto" Carvalhaes/Pedro Solberg is 1-0 and Robin Seidl/Tobias Winter of Austria is 0-1.
Up next for the United States is Brazil while South Africa plays Austria. Both matches are Wednesday, 2 August.