Both teams will arrive at Stade de France with unbeaten tournament records.
South Africa comfortably topped England's qualifying pool, smashing the world champions 36-0 on their way through, while Argentina dominated a group that also included France and Ireland.
All 11 previous games between South Africa and Argentina went the the Springboks' way, including seven wins in Buenos Aires, where teams like England and France have previously come unstuck.
Smit though, has urged caution as South Africa look to reach their first World Cup final since 1995.
He said: "We have tweaked one or two things for this game, and Sunday will tell whether we've analysed them (Argentina) in the right way.
"Time will tell if we have done enough homework.
"We are under no illusions that it will be tough after what they have done in this World Cup.
"What I like about them is they don't rely on individuals.
"They have some fantastic individuals, but the way they play, they work as a team. They have fantastic forwards and backs that chase the ball and put their bodies on the line."
Springboks coach Jake White has made one change for the game, recalling fit-again prop CJ van der Linde following his recovery from a knee injury, while Argentina retain the side that accounted for quarter-final opponents Scotland.
South Africa would realistically expected to meet Australia or New Zealand in the final next Saturday, but both made quarter-final exits at the respective hands of England and France.
And Smit added: "It makes you realise what the World Cup means when you get to the knockout phase.
"The quarter-finals are one of the hardest rounds to play. Of the eight teams involved, I don't think anyone played their best rugby.
"To see the two top teams go out, it makes you realise there is a lot to play for. They were beaten by two teams who are still in, and who can play under pressure."
Performing under pressure was something South Africa successfully managed during the closing quarter of a tricky quarter-final against Fiji, scoring 17 unanswered points, and they have now replaced New Zealand as tournament favourites.
Springboks full-back Percy Montgomery said: "There has been a lot of planning since 2004. Jake (White) has done a lot of building for this match at the Stade de France.
"We've just got to keep the ball on Sunday, that's the most important bit.
"Argentina's strength is their forwards, but they have pretty good backs too. Anything can happen.
"We've got to get them to play the way we want to play, and force them to play the way we want to play."