After their humbling at home last weekend, Argentina appeared to be struggling again in the first half in Pretoria. But an intercept try by lock Guido Petti right on half-time and against the run of play gave the Pumas hope — and a surprise 10-8 lead at the break.
Captain Pablo Matera scored in the second half to make it 18-18 and raise the possibility of a first win in South Africa since 2015.
Jantjies' two late penalties denied Argentina and completed a solid night for the backup No 10.
Argentina missed crucial opportunities as well as having the dramatic late try disallowed. Wing Sebastian Cancelliere knocked on a pass a meter from the tryline early in the second half and before Nkosi's second try. And replacement first-five Benjamin Urdapilleta missed a conversion and a penalty in the late stages.
At 21-18 to South Africa, Urdapilleta started the move that ended with Mensa slicing through a splintered South Africa defence with three minutes to go to score next to the posts and apparently snatch a shock victory. But the referee reviewed TV replays and decided Argentina's Jeronimo De La Fuente obstructed South Africa prop Vincent Koch and prevented him making a tackle on Urdapilleta early in the counter.
Argentina's disappointment was tempered by the fact it was a much-improved performance, especially up front, from Salta.
"The game could have gone to either of the teams. Unlucky for us tonight," Matera said. "The World Cup is coming, everything is positive.
"We were stronger than the Springboks in the scrum today. Very different to last week."
South Africa gave up the first-half lead while on the attack after the hooter when halfback Cobus Reinach threw an optimistic pass and second-rower Petti snapped it up and ran more than 50 meters the other way, the big man outpacing the Springboks cover. Matera went over with 15 minutes to go to level the scores and force South Africa to dig deep.
- AP