It's a test of depth at the start of a Rugby World Cup season.

South Africa's largely experimental lineup in the first round of a shortened Rugby Championship is by choice. Australia's is mainly enforced by a hefty injury list and the firing of star player Israel Folau, although the Wallabies have also sprung a couple of selection surprises.

Whatever the reason, both have the opportunity to look at new players and new combinations when they meet on Saturday at Ellis Park. They are two months out from a World Cup where both fear losing ground in the race to be among the top challengers to the world champion All Blacks.

Australia coach Michael Cheika came under serious pressure for his job last season. He held on but starts this year's World Cup buildup without Folau, midfield playmaker Kurtley Beale and scrumhalf Will Genia, previously the first names on Cheika's team sheet.

Folau was fired by Australian rugby for homophobic comments on social media and the Wallabies must move on. Beale and Genia were named on the bench for the game in Johannesburg, a surprise from Cheika considering the loss of Folau left a huge hole in the backline.

Cheika is trying out a center combination that offers a different approach to previous Wallabies lineups. Samu Kerevi and Tevita Kuridrani are hard-running, physical and direct and employ a contrasting style to the subtle skills of Beale. There's no harm in trying out a Plan B for the World Cup.

Tom Banks has the unenviable task of replacing try-scoring wonder Folau at fullback.

As always, Australia needs to match the Boks up front if it's to make any progress.

Melbourne's Isi Nairarani will make his debut at No. 8 and veteran James Slipper returns to the front row for the first time since he was suspended a little over a year ago for twice testing positive for cocaine.

It appears to be an uphill task for the Wallabies at Ellis Park, where they haven't won since 1963.

"We've got to earn everything this year," Cheika said. "We know a lot of people aren't giving us much of a chance this season but I believe in our players."

One man not so down on the Wallabies' chances is Springboks coach Rassie Erasmus, who said Australia always "get it right" in a World Cup year.

Yet Erasmus has chosen South Africa's only home test of the Rugby Championship as the opportunity to change things up and gauge his options. He might be taking a bigger risk than Cheika. South Africa is expected to win, so failure would be a much bigger blow to the World Cup preparations.

Erasmus sent a group of senior players including hooker Malcolm Marx, loose forward Duane Vermeulen, scrumhalf Faf de Klerk, flyhalf Handre Pollard and fullback Willie le Roux ahead to New Zealand to prepare for next weekend against the world champions.

At Ellis Park, the Springboks will be a mix of those returning from injury and needing game time, and fringe players pushing for places at the World Cup.

Scrumhalf Herschel Jantjies makes his test debut in a whirlwind rise having started the season as a reserve player for his Super Rugby franchise. Flanker Rynhardt Elstadt was also selected for his debut in a starting team that's very different to Erasmus' first-choice 15.

Erasmus reassured everyone that he has "a specific plan" to balance the demands of a back-to-back Rugby Championship and World Cup.

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Lineups:

South Africa: Warrick Gelant, Sbu Nkosi, Jesse Kriel, Andre Esterhuizen, Makazole Mapimpi, Elton Jantjies, Herschel Jantjies; Francois Louw, Pieter-Steph du Toit, Rynhardt Elstadt, Lood de Jager, Eben Etzebeth (captain), Trevor Nyakane, Bongi Mbonambi, Tendai Mtawarira. Reserves: Schalk Brit, Lizo Gqoboka, Vincent Koch, Marvin Orie, Marcell Coetzee, Cobus Reinach, Frans Steyn, Dillyn Leyds.

Australia: Tom Banks, Dane Haylett-Petty, Tevita Kuridrani, Samu Kerevi, Reece Hodge, Bernard Foley, Nic White; Isi Nairarani, Michael Hooper (captain), Lukhan Salakaia-Loto, Rory Arnold, Izack Rodda, Sekope Kepu, Folau Fainga'a, James Slipper. Reserves: Jordan Uelese, Harry Johnson-Holmes, Taniela Tupou, Rob Simmons, Jack Dempsey, Will Genia, Matt To'omua, Kurtley Beale.

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