“We just wanted to play good rugby – put the work we have done in training into the game.”
Feinberg-Mngomezulu scored two tries in the first half, but the hosts led by only two points at half-time.
Malcolm Marx scored South Africa’s other first-half try, but Argentina countered with a score from Santiago Chocobares, who walked the ball between the posts after an inexplicable mistake from winger Cheslin Kolbe, and a penalty try.
Fly-half Santiago Carreras added a conversion and three penalties to keep Argentina in contention.
But South Africa pulled away in the second half as Kolbe, Feinberg-Mngomezulu, Pieter-Steph du Toit, Morne van den Berg and Manie Libbok went over in front of a raucous 45,000-strong crowd.
A bonus-point win next week would secure South Africa a third Rugby Championship in its current format, but they will win the title if Australia beat New Zealand.
