The Australians will take on the wounded Pumas in San Juan on Sunday morning (AEST) looking to back up last week's rousing 41-26 victory.

With 63 Test caps under his belt, O'Connor has taken over the No.10 jersey vacated after Quade Cooper ruptured his achilles with Reece Hodge, who came on in Mendoza, again starting on the bench.

It's a chance for O'Connor to make his mark leading into next year's Rugby World Cup in France.

"Obviously with Quade gone, no Hoops (Michael Hooper), no Allan (Alaalatoa) we were keen to get a bit of experience out there," Rennie said on Friday after naming his team.

"He's an important voice in amongst our backline so he's prepared really well, he's really excited to get a crack.

"He's keen to get out there and prove that he's got plenty more footy in him."

O'Connor's last Test was an unhappy one, making a series of errors after coming off the bench in Australia's loss to England in Brisbane.

Rennie said he had "sharpened up" his acceleration and skill set since then to press his claims for selection ahead of youngster Noah Lolesio.

The decision was reinforced when inside centre Hunter Paisami picked up a concussion from game one, with Rennie opting for Waratahs back Lalakai Foketi for his first start, partnering Len Ikitau.

"He's a good athlete, good feet," Rennie said of the 27-year-old Foketi.

"He's worked really hard on his defensive game and his post tackle and his kicking and made good shifts so we're excited."

Prop James Slipper will again lead the side in the absence of skipper Hooper, while Taniela Tupou replaces Alaalatoa, who became the fourth member from the Wallabies squad to fly home from Argentina following a family bereavement.

"Giteau's Law" choice Rory Arnold, who has been based in France, will have his first start of the year in the second row, replacing Matt Philip.

Rennie said he'd left Philip out entirely for him to freshen up, wanting to give young bulls Darcy Swain and Nick Frost another run.

Adding to his 29 caps, Arnold has overcome a calf niggle to suit up.

"He looks good, he's a big man, he's experienced," Rennie said of Arnold.

"He's a big target, a fantastic lineout forward, very good maul and maul defence so it's set piece that we want a lot out of him."

Giant Melbourne enforcer Pone Fa'amausili has been named to make his Test debut from the bench after a series of injury setbacks.

"He's a massive man and when Taniela (Tupou) comes off we're going to replace him with someone who's of pretty similar dimensions," Rennie said.

Irae Simone, who was a late call-up to the squad and will head to France following the two-Test tour of Argentina, has been named on the bench for his third Test with Rennie adding an additional back.

Rennie said with O'Connor's lack of game time and the inexperience of his midfield it was "insurance".

Pumas head coach Michael Cheika made four changes to his line-up, with three coming in the backline including Gonzalo Bertranou taking over the starting halfback role from Tomas Cubelli.

Wallabies: Tom Wright, Jordan Petaia, Len Ikitau, Lalakai Foketi, Marika Koroibete, James O'Connor, Nic White, Rob Valetini, Fraser McReight, Jed Holloway, Darcy Swain, Rory Arnold, Taniela Tupou, Folau Fainga'a, James Slipper (c). Res: Lachlan Lonergan, Matt Gibbon, Pone Fa'amausili, Nick Frost, Pete Samu, Tate McDermott, Irae Simone, Reece Hodge.

Australian Associated Press