Fly-half Manie Libbok scored a breakaway try against the run of play to secure South Africa a bruising 22-21 victory over Argentina and earn a second-place finish in the Rugby Championship at Ellis Park on Saturday.The Springboks had to withstand heavy Argentine pressure, some of their own making through poor execution, but managed to grind out the win as they also scored tries through lock Eben Etzebeth and centre Damian de Allende.Argentina were in the contest all the way but battled to break down the resolute home defence and got tries late on through wing Mateo Carreras and replacement Gonzalo Bertranou as the visitors pushed for what would have been a first ever win in Johannesburg.New Zealand claimed the Rugby Championship trophy earlier on Saturday with a comprehensive 38-7 victory over Australia in Melbourne but the Boks' victory sees them end second, with Argentina in third.