Flank Willem Alberts scored the bonus-point fourth try and De Villiers, scrumhalf Fourie du Preez, left wing Bryan Habana, No. 8 Duane Vermeulen and replacement hooker Bismarck du Plessis also dotted down.
Steyn missed only one of the conversions as he lifted his personal tally to 28 points and a nine-point lead over Australia’s Christian Leali’ifano in the individual scoring charts.
Contepomi, leading the team in the absence of injured No. 8 Juan Martin Fernandez Lobbe, went over in the final minute for the lone Argentina try, which he converted.