Australia's most-capped prop, Al Baxter, stands at the crossroads of a turbulent career after Robbie Deans signalled a changing of the guard at tighthead.

Baxter will be a notable absentee from the Wallabies starting pack for Saturday night's Tri-Nations clash against South Africa, with Test rookie Ben Alexander preferred in the front-row.

A converted loose-head, Alexander has proved a revelation on the other side of the scrum to repay Deans' major 2009 selection gamble.

The Brumbies prop has made every post a winner, including a storming second-half scrummaging display in Australia's 29-17 loss to the Springboks at Cape Town earlier this month, while Baxter has been punished for the countless collapses on his side of the scrum.

The 32-year-old, who last year rebuilt his tattered reputation with a powerful spring tour, has been on the receiving end of the referees' wrath in the Tri-Nations.

Deans hooked Baxter, capped 69 times, after half an hour in the 19-18 loss to New Zealand, and showed his patience had worn out on Thursday by naming him on the bench.

The coach admitted the Subiaco Oval selection would be viewed as a changing of the guard.

"I've got no doubt Al will be looking at it and feeling it to that end," Deans said. "And I've got no doubt that Benny A will be hoping that that's the case and will be wanting to make the most of the opportunity.

"But in terms of what happens from this point on, we don't know. It depends very much on what both those blokes bring to the table."

There has been a stream of thought Baxter has been unfairly punished by whistleblowers with a perception he's an inferior scrummager, but Deans was clear any injustices still hurt his side.

"Perceived (problems) become real and once again Al owns part of that and he's conceded as much himself," he said.

"You just can't leave your destiny in the hands of a third party and to some extent he has."

Deans' tight-head experiment - by plugging for the destructive Alexander - has been Australia's surprise success story of a largely disappointing Tri-Nations campaign.

The 24-year-old was initially picked as the back-up to Baxter in a squad that contained three specialist loose-heads.

"He's done more than cope in every instance, he's actually made a difference to our scrum every time he's come on," Deans said.

"We've consciously graduated his entry because you want those experiences to be good for all those players."

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