Santiago Gonzalez Iglesias kicked a 78th-minute penalty as South Africa's hopes of Rugby Championship glory were dealt a huge blow with a shock 26-24 defeat to Argentina on Saturday.
The Springboks narrowly avoided a disappointing draw with the Pumas in their tournament opener in Nelspruit last weekend, winning 30-23 with a last-gasp try.
But they could not overcome another spirited effort from Argentina in Salta, the South Americans emerging victorious at the end of a frenetic encounter.
Bryan Habana crossed for a world-record 65th Test try to help South Africa fight back after they had gone into half-time 13-3 down and the Springboks appeared on course for the points after turning a 23-13 deficit into a one-point lead despite Morne Steyn failing to convert Pieter-Steph du Toit's score.
But Steyn's miss did eventually prove pivotal, as Gonzalez Iglesias held his nerve and Argentina stood firm in a tense finale, leaving Allister Coetzee's men with an uphill battle to win the title with New Zealand having claimed two comfortable victories over Australia.
Argentina had an early chance to open the scoring in the 17th minute when Manuel Montero looked to have crossed from a five-metre scrum but was unable to keep control of the ball.
The hosts then had prop Ramiro Herrera sin-binned for a bad tackle on Francois Louw, and Elton Jantjies converted the resulting penalty to give South Africa a 3-0 lead.
However, straight after the restart South Africa were pinned for not releasing and Nicolas Sanchez duly levelled the scores before making it 6-3 with another three-pointer on the half-hour mark.
Montero had been denied by a try-saving tackle prior to the fly-half's second penalty, but the wing turned provider with a superb offload to Joaquin Tuculet, whose score was duly converted by Sanchez.
South Africa scored 10 points in six second-half minutes to erase the advantage Argentina held at the interval, Jantjies knocking over a penalty before wing Habana wrote his name into the history books.
Johan Goosen added the extras but Argentina's response was swift, Juan Manuel Leguizamon beating Habana in the air to touch down from Juan Martin Hernandez's up and under.
Hernandez's subsequent conversion and 54th-minute penalty had Argentina in command again but Steyn reduced the arrears to seven with the boot.
A clash of heads with Oupa Mohoje led to Hernandez being taken off on a stretcher with a neck brace on and things began to look ominous once more for Argentina as Jaco Kriel fed Du Toit for South Africa's second try.
Steyn's missed conversion looked like it would be immaterial after he made amends with his second penalty but the Springboks could not keep their discipline, allowing Gonzalez Iglesias to step up and seal a famous triumph.