It was a first win over Argentina at this age level and there was instant success for wing Steve Davies (UWIC/Llanelli Scarlets) as he flew in for the injured Ricky Williams (Llandovery Coll) and scored the opening try and later notched the third Wales touchdown.
Aled Thomas (Carmarthen Quins) had been switched to full back and he landed two conversions and a penalty goal, while further tries came from lock Alun Wyn Jones (Llandovery Coll) and Aled Brew (Neath Coll), the latter being the younger bother of senior cap Nathan Brew.
Wales now meet Scotland in the play-offs for fifth to eighth spots. The winners of that match will meet the winners of Australia vs Japan for the fifth-sixth positions.