Mike Phillips and George North scored first-half tries, while Leigh Halfpenny kicked 13 points in the opening period.
Argentine flyhalf Nicolas Sanchez did pull a penalty back for the visitors, but it was Wales who led 23-3 at the break.
Halfpenny and Sanchez traded penalties at the start of the second period, before Toby Faletau and replacement hooker Ken Owens touched down.
Welsh kicking sensation Halfpenny converted both tries and another penalty to take his personal haul to 20 points.
In other internationals on Saturday, Australia defeated Ireland 32-15, France beat Tonga 38-18 and Italy were victorious over Fiji 37-31.