The Springboks take on a Welsh side determined to avenge June's 18-53 Test mauling in Pretoria, but Smit says his players are in no mood to lose that winning feeling.
'Confidence is the most powerful tool any team can have, and we have," the 34-times capped hooker said at a press conference in the team's Hilton Hotel in Cardiff. 'The last two or three years haven't been pretty for South African rugby, but (coach) Jake White has come in with a completely different approach.
'He's given us the tools to fight the war with. We are confident, but we don't consider ourselves favourites to complete the Grand Slam - we feel we have to improve a couple of levels to do that.'
Springbok coach White said he was expecting a "completely different" Wales team to the one which was out-classed in Pretoria in June.
'They were missing a few key players on that tour, and then Brent Cockbain had to go home because of his personal tragedy,' he said, referring to the death of the Australian-born lock's one-year-old son Toby.
'As well, Michael Owen had to pull out with injury, so they're a completely different team this weekend. Having said that, our fullback Percy Montgomery knows how Mike Ruddock operates from their time together at Newport, and I don't think he'll go away from the things that work best for him.'
White admitted he wanted his pack to out-muscle the opposition on Saturday.
'We are expecting to win this up front,' he said. 'South African guys have always been big and strong, and we've gone back to that this year. We're also lucky in that if you look at our forwards, they're all very athletic, so we have size and speed.'
White said the opportunity to win a "Grand Slam" of victories over Wales, Ireland, England and Scotland was too good to pass up.
'It hasn't been done by a South African team since 1961, and some great Springbok teams have never had the opportunity to achieve it, but we have to be realistic - this is a very young team.
'This year's achievements have already surpassed expectations, but I've told the players what a great opportunity they have to write their names in the history books.
'We have to start well against Wales - the whole of South Africa is watching to see if we can continue where we left off at Kings Park when we won the Tri-Nations title.'
Wales have beaten South Africa only once in 17 matches dating back to 1906. They won 29-19 at the Millennium Stadium in 1998, with legendary fly-half Neil Jenkins kicking 19 points.
Teams (kick-off 2.45pm):
Wales: G Thomas (capt); H Luscombe, S Parker, G Henson, S Williams; Stephen Jones, D Peel; Duncan Jones, Steve Jones, A Jones, B Cockbain, M Owen, Dafydd Jones, C Charvis, R Jones
Replacements: M Davies, G Jenkins, L Charteris, M Williams, M Phillips, C Sweeney, T Shanklin
South Africa: P Montgomery; B Paulse, M Joubert, De Wet Barry, A Willemse; J van der Westhuizen, F du Preez; O du Randt, J Smit (capt), E Andrews, B Botha, V Matfield, S Burger, J van Niekerk, J Smith
Replacements: H Shimange; C J van der Linde, G Britz, T Dlulane, M Claassens, J de Villiers, B Russell/G du Toit