Cecil Afrika scored a hat-trick to take his day one try tally to five in South Africa's 29-12 victory against reigning Rugby World Cup Sevens champions Wales.
Frankie Horne and Kyle Brown also raced over while in reply Rhys Shellard and Lee Williams hit back for Wales with Alex Walker adding a conversion
A Walker conversion proved the difference for Wales in their narrow 14-12 victory against Dubai Sevens runners-up France.
Trailing 12-7 after tries from Paul Albaladejo and Julien Jane, Lee Williams raced away to cross the line before Walker converted to take the win.
The victory gives Wales a chance of making the knock out stages, but they will have to pile the points on Uruguay and hope South Africa do them a favour by beating France.
Uruguay narrowly missed out on an upset against France, eventually losing 21-19. Two Felipe Berchesi tries and one from Guillermo Lijtenstein gave them a 19-14 lead but Terry Bouhraoua's try and Thibaut Zambelli's conversion snatched a late victory for France.
New Zealand, Samoa, Fiji, South Africa, Kenya and England all remain unbeaten after the opening day of action at the USA Sevens, round five of the HSBC Sevens World Series in Las Vegas.
Of those sides, New Zealand, Samoa, Kenya and England are mathematically guaranteed a place in the Cup quarter finals.
In a changed format for the USA round of the Series, each of the 16 teams played two of their three pool matches on Friday evening at the Sam Boyd Stadium.
On Saturday 11 February they will play their remaining pool match and then a quarter final in either the Cup or the Bowl, leaving the climax of the knock-out competition on Sunday 12 February.