Hooker Schalk Brits will play at number eight for the first time in more than a decade when South Africa take on minnows Namibia on Saturday.
The former Saracen, 38, retired in 2018 but was convinced to return to rugby by Springboks coach Rassie Erasmus.
Elsewhere Herschel Jantjies and Elton Jantjies replace rested half-back pair Faf de Klerk and Handre Pollard.
Namibia make 10 personnel changes from the team that lost to Italy, but centre Johan Deysel only makes the bench.
Deysel, who scored Namibia's only try in their 58-14 defeat by eventual champions New Zealand at the 2015 tournament, missed his team's Pool B opener with a shoulder problem.
The Springboks have also made wholesale changes from the team that lost to New Zealand on Saturday with only centre Lukhanyo Am and wing Makazole Mapimpi retaining their places.
Bath flanker Francois Louw, Saracens prop Vincent Koch and Sale-bound second row Lood de Jager all come into the forwards, while S'Busiso Nkosi, who has scored seven tries in eight Test appearances, is named on the wing.
Namibia have trained with South-African provincial side the Sharks and played in South Africa's domestic Currie Cup competition as they seek to improve on defeats by their neighbour of 105-13 (just before the 2007 World Cup) and 87-0 at the 2011 tournament.
Teams:
South Africa: Gelant; Nkosi, Am, Steyn, Mapimpi; E Jantjies, H Jantjies; Mtawarira, Mbonambi, Koch; Snyman, De Jager, Louw; Smith, Brits.
Replacments: Kitshoff, T Du Toit, Etzebeth, Kolisi, Mostert, Reinach, De Allende, Kolbe
Namibia: Tromp; Plato, Greyling, Walters, Klim; Loubser, Jantjies; Sethie, Van der Westhuizen, De Klerk; Retief, Uanivi, Forbes; Katjijeko, Booysen
Replacements: Nortje, Rademeyer, Coetzee, Gaoseb, Venter, Conradie, Axasman Kisting, Deysel.
What they said:
South Africa number eight Schalk Brits on his return to rugby: "When Rassie spoke to me I was sipping cocktails in Ibiza.
"I can always do an 8am-5pm job, but I can't always play. It's been a great decision. It is unbelievable to be part of this group of players.
"When you consider where we were 18 months ago to where we are now, it has been an upward path."
Namibia centre Justin Newman: "Studying in South Africa and watching them on TV, I always wondered what it would be like playing against them so I am excited to compare myself with guys I never thought I would.
"To see how they play, to see the level they play at. They are just flesh and blood but it will be an awesome experience."