After the All Blacks beat the Wallabies by 40-14 in Auckland on Saturday morning, the Boks had to win with a bonus point and a points' difference of at least 39, and they failed on both accounts, but still finished the competition with four wins from six games, the same as New Zealand.
The Boks dominated the first half and built up a well-deserved 17-7 lead but Argentina never allowed the home side to run away with proceedings and managed to stay in the fight throughout, although their discipline got the better of them as illustrated by the four yellow cards dished out to the visitors for an assortment of transgressions, while the Boks had two men sent to the sin bin in a stop-start affair that was played in tricky conditions.
Experienced lock Eben Etzebeth thought he had scored when he went over in the 10th minute, however, he received the ball from an offside position in the maul and the try was ruled out.
Not long thereafter, Pumas flank Marcos Kremer was yellow carded for offside play with the Boks on the attack. The green and gold jerseys finally got onto the scoreboard through hard-working No 8 Jasper Wiese, who had the simple task to dot the ball down from a powerful Bok scrum.
Steyn’s conversion handed the home side a well-deserved 7-0 lead at the halfway mark of the opening half. With the Boks making Argentina sweat on defence and piling on the pressure upfront, Juan Martin Gonzalez was also sent to the sin bin for repeated offsides, while Willie le Roux was held up on the whitewash in the next movement.
However, the South Africans kept piling on the pressure and it was no surprise when skipper Siya Kolisi went over following another powerful lineout maul to hand his side a 14-0 lead.
Steyn, playing at flyhalf for the Boks for the first time since 2008, then slotted a long range penalty kick to make it 17-0.
However, the South Americans scored their first try on the stroke of halftime through scrumhalf Gonzalo Bertranou, which Emiliano Boffelli converted to make the score at the break 17-7.
The Pumas came back strongly in the second half and Juan Martín González got their second try seven minutes after the restart as he raced past Le Roux to score out wide. When Boffelli slotted the difficult conversion, he narrowed the deficit to 17-14.
Both teams then made numerous changes, with the Springboks sending on Duane Vermeulen and Kwagga Smith, amongst others, in an effort to continue their dominance upfront. The Bok forwards then forced their first penalty try as they mauled powerfully towards the Argentine goal line, and Jeronimo de la Fuente was issued a yellow card his indiscretion during that movement.
Etzebeth was then yellow carded for dangerous play, with both sides now playing with 14 men and with rain falling down, the Boks had to fight hard to keep their 24-14 lead intact.
However, the Boks were then down to 13 men when replacement scrumhalf Faf de Klerk was shown yellow for a cynical offence, which stopped a goal-bound Argentine maul.
Matias Moroni then scored out side, with Boffelli's conversion pulling the Pumas back to within three points and time running out on the clock, but the Boks still had some gas left in the tank and got themselves into a strong field position.
Launching yet another maul at the Argentinean tryline, Pumas reserve prop Joel Sclavi also got his marching orders after trying to stop a maul illegally, and the Boks were awarded a second penalty try in the process, which allowed the South Africans some breathing space with the score now 31-21 in their favour and less than 10 minutes left on the clock.
With time up, replacement wing Kurt-Lee Arendse was sent over for the Boks’ fifth try - and his second in only his third Test - with speedsters Makazole Mapimpi and Canan Moodie both featuring prominently. Steyn added the extras for the Springboks to record their fourth win of the campaign.
Springboks 38 (17) – Tries: Jasper Wiese, Siya Kolisi, Penalty tries (2), Kurt-Lee Arendse. Conversions: Frans Steyn (3). Penalty goal: Steyn.
Argentina 21 (7) – Tries: Gonzalo Bertranou, Juan Martín González, Matías Moroni. Conversions: Emiliano Boffelli (3).