Williams will win his 87th and final Wales cap at the Millennium Stadium before retiring from the Test arena three months short of his 35th birthday.
The Ospreys wing has scored a Wales record 57 tries, featured in two Six Nations Grand Slam-winning seasons and was part of three World Cup campaigns.
He will bow out as a genuine Wales great and Deans believes the home team's desire to give Williams a victorious send-off should not be underestimated.
"We experienced ourselves how powerful the additional motivation of playing for a mate can be when 'Sharpie' (Wallabies lock Nathan Sharpe) had his 100th Test in Auckland (against Wales) recently," Deans said.
"There was no way any of the other players wanted to let him down.
"I have no doubts that the Welsh lads will be feeling just the same this week as we did in Auckland. Emotion plays a powerful role in competitive sport."
After winning just once in four visits to Cardiff between 2005 and 2008, Australia will bid for a third successive Millennium Stadium victory over Wales this weekend.
They also triumphed when the countries last met in the World Cup bronze medal match at Eden Park 41 days ago, but Deans is to face a searching examination.
"Warren (Gatland, Wales coach) will be looking for his group to push on from the World Cup," Deans added.
"And this match provides him with a perfect opportunity to do just that as a springboard heading into the next Six Nations Championship."
James O'Connor, meanwhile, will make his first Test match start at fly-half on Saturday.
The goalkicking wing impressed at number 10 against the Barbarians at Twickenham last weekend - Australia won 60-11 - and Deans has retained him in that pivotal role.
However, O'Connor has big boots to fill as he takes over from Australia's World Cup fly-half Quade Cooper, who is currently recovering after suffering a serious knee injury during the World Cup play-off encounter.
Elsewhere, centre Berrick Barnes has recovered after taking a blow to his back to start alongside Rob Horne in midfield, while lock Rob Simmons replaces Sharpe.
Simmons for Sharpe is the only change up front from when the countries last met.
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