New Wallabies captain Ben Mowen is the "right guy at the right time" to lead the team out of a slump and coach Ewen McKenzie has backed his "demanding" leadership to deliver a Test victory on Saturday night.

Mowen was installed as captain while half-back Will Genia was dumped to the Wallabies bench on Wednesday as McKenzie searches for a spark to end a four-match losing streak.

In a sign that no one is safe in the Wallabies line-up, McKenzie axed Genia - one of the world's best No.9s - in the hope it will motivate him to rediscover his world-class form.

That leaves six-Test Wallaby Mowen as the man in charge of resurrecting the Wallabies' Rugby Championship campaign.

It's a remarkable turnaround from the player who was on the outer with the NSW Waratahs in 2011 and appeared unlikely to ever play for Australia.

"There would have been time when [Mowen] thought he was going nowhere, that he was just treading water in Australian rugby," McKenzie said.

"Things change. He's got his own style of leadership, he's very definite about things. Some of those things will give us an outcome.

"He's the right guy at the right time. What he does with the opportunity, we'll wait and see. He's already imposed himself at training ... he's demanding and once you set a standard he'll make sure the guys stick to it."

With Genia and regular captain James Horwill (hamstring) out, Adam Ashley-Cooper will step up as vice-captain.

McKenzie said dropping Genia was about making "hard decisions" to try to get the win the Wallabies desperately crave.

McKenzie has lost all three matches as Wallabies coach since taking over from Robbie Deans in July.

"We have to keep looking for things to spark the team up to get an outcome. We're not in the business of hoping things get better. We're in the business of driving outcomes," McKenzie said.

McKenzie has made four changes to his 23-man squad as the Wallabies prepare to take on Argentina in Perth.

Nic White replaces Genia at halfback and Ben Alexander returns to the starting XV as the tighthead prop.

Giant forward Sitaleki Timani is on the bench to add muscle after the Wallabies were bashed last weekend, and outside back Tevita Kuridrani is a reserve.

Mowen has transformed his career since joining the Brumbies at the start of last year and made his Test debut in June.

The former Waratah and Queensland Red has found his feet at the Brumbies and led the team into the Super Rugby final last month.

At the start of the season and seemingly on the outer with Robbie Deans, Mowen contemplated leaving Australian rugby to sign a lucrative contract in Japan.

But he decided to stay to chase his Wallabies dream and it's paying dividends.