Both sides are currently a perfect three from three in the Pool A, having beaten hosts England on back-to-back weekends at Twickenham.
They both return to Rugby HQ this weekend and Gatland has rung the changes for his Wales side, including pairing up 2013 British & Irish Lions George North and Jamie Roberts in the centres.
That means Liam Williams shifts to left wing and Gareth Anscombe comes in at full-back - the half-back pairing of Dan Biggar and Gareth Davies remains in place.
All-star Lions trio of Sam Warburton, Justin Tipuric and Taulupe Faletau form the back-row, while fellow tourist Dan Lydiate misses out on the clash due to the bruised eye socket he sustained against Fiji.
Ever-present second-row Alun Wyn Jones also starts and Gatland knows that Wales' World Cup campaign will only get harder from here on in.
"Saturday is another huge encounter and both sides will be coming in with momentum and looking to top Pool A," said Gatland.
"We have been impressed with Australia so far in this competition and we know a step up is required at Twickenham this weekend.
"It is still all to play for in terms of the knock-out phases.
"We've trained well this week, had a full squad to pick from and it is great to welcome back players from injury."
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