The Blitzboks beat USA 24-17 to advance to the Cup quarter-finals as the top seeds from their pool at the Spain Sevens on Saturday.
Coming into this clash, South Africa were on a 30-game winning streak and were odds-on favourites to continue their winning ways.
But they didn’t have it all their own way as the result of this showdown hung in the balance until the very end.
USA captain Kevon Williams scored a first-half brace to give his team an unexpected 12-7 lead the break.
Dewald Human crossed the line for the Blitzboks’ sole try.
The South Africans made a much-better start to the second half, patiently rotating possession before Christie Grobbelaar scuttled over to score in the corner.
The USA then launched an attack from the restart, but a handling mistake by Perry Baker was pounced on by the Blitzboks, who went on to score through Shaun Williams.
With the game on a knife’s edge and USA in possession, Williams was again in the thick of things as he effected a turnover penalty on the ground and then scored from the resultant quick tap to double South Africa’s lead.
USA would finish with a flourish as Baker ran in a late try, but that was just a consolation.
South Africa will face Scotland in the quarter-finals later on Saturday night.