South Africa showed their real potential for only 20 minutes of Saturday's 34-21 win over Argentina in the Rugby Championship but it was on expected lines with several key players returning after layoffs, according to coach Rassie Erasmus.

Players like Eben Etzebeth, Malcolm Marx and Warren Whiteley were in the side after missing June's three tests against England while England-based Faf de Klerk and Francois Louw were fresh from post-season holidays.

It made for a disjointed and error-ridden showing at Kings' Park although in the end pure force and aggression saw the Springboks to a comfortable bonus-point victory.

Erasmus said South Africa had their momentum stymied by the Pumas who were effective in slowing down the ball but "lucky the boys fixed it in the second half".

Yet again, they were forced to rally in the second half after going into the break 14-10 down but eventually outscored their visitors by six tries to three. 

"There were some technical errors, particularly in the line-ups but the pack put on a dominant performance, maybe not the most crisp and perfect," the new Springbok coach added.

Erasmus rued five botched line outs close to the Pumas try line after the Boks had turned down penalty opportunities to rather go for tries.

"It was terrible to lose line outs inside their 22. That's terrible, you can't do that," he said. "We didn't capitalise on any of the five times we were right there in the first half."