Wallabies coach Ewen McKenzie hates axing players.

But he hates losing even more.

McKenzie made one of the hardest decisions of his coaching career this week when he relegated star scrumhalf Will Genia to the bench for Saturday night's clash with Argentina in Perth.

Genia has failed to produce his usual heroics during the Wallabies' four-match losing run, but he was far from the team's worst in last week's 38-12 loss to South Africa in Brisbane.

With captain James Horwill still nursing a hamstring injury and Genia demoted to the bench, Brumbies' No.8 Ben Mowen will take over as skipper in what will be just his seventh Test.

Brumbies scrumhalf Nic White earns his first Test start and fourth cap overall.

McKenzie is feeling the heat after overseeing three straight losses since taking over as coach from Robbie Deans.

The former Reds boss is confident positive results will soon come.

And although he didn't enjoy telling Genia of his axing, he won't be afraid to make more tough calls if the Wallabies' form doesn't improve soon.

Five-eighth Quade Cooper could be the next to fall if he fails to fire against the Pumas on Saturday.

"As a leader, you get defined by the decisions you make, not the ones you avoid," McKenzie said on Wednesday.

"Everyone can make easy decisions. It's the hard ones that make a difference.

"I hate losing. I'm not enjoying this time at all.

"But I'm not sitting around hoping something is going to change.

"I'm actually in there trying to drive an outcome.

"I won't leave any stone unturned. I'll keep looking, and if it means you've got to make hard decisions, then you've got to make hard decisions."

McKenzie said Genia was disappointed to learn of his axing.

But he backed the 25-year-old to rebound strongly.

"I know it's the right decision for now. I also know Will will respond. I know his qualities," said McKenzie, who also coached Genia at the Reds.

"It's been a long time since he's been in this situation.

"Will's an outstanding player. But he'd admit he hasn't been at the peak of his game of late."

In the only other change to the starting line-up, prop Ben Alexander replaces Sekope Kepu as the Wallabies attempt to fix up their scrum problems from last week.

Powerhouse lock Sitaleki Timani has been named on the bench, with Brumbies back Tevita Kuridrani the other inclusion on the pine.

McKenzie threatened to dumb down his tactics following last week's shellacking from South Africa.

But he's softened his approach somewhat this week, instead stressing the need to play smarter and make better decisions about when to unleash the backs.

Wallabies: Israel Folau, James O'Connor, Adam Ashley-Cooper, Christian Leali'ifano, Nick Cummins, Quade Cooper, Nic White; Ben Mowen (capt), Michael Hooper, Scott Fardy, Kane Douglas, Rob Simmons, Ben Alexander, Stephen Moore, James Slipper. Res: Saia Fainga'a, Scott Sio, Sekope Kepu, Sitaleki Timani, Ben McCalman, Will Genia, Matt Toomua, Tevita Kuridrani.