The two teams go ahead-to-head in a match that will determine who finish top of Pool A and avoid South Africa in the quarterfinal.
Both sides, who've each beaten knocked-out tournament hosts England in the 'Pool of Death', have already qualified for the quarterfinals.
Wales have not beaten Australia since 2008 but their last five meetings have seen them lose by just a single score.
"We haven’t spoken about it at all," Gatland told reporters at Wales' Weybridge training base, south-west of London.
"The last five times there’s been a score in it. We've been ahead in games and not been able to finish it off," the New Zealander added.
But he cited Wales' 12-6 win over South Africa in November and their recent 28-25 World Cup defeat of England, where they were three times down by 10 points, as proof of his team's increasing ability to deal with pressure situations.
"You learn from that. Experience comes from that and that showed in the last big game in the autumn versus South Africa, we closed that game down and were brilliant in the last 15 minutes.
"Against England, coming from behind and the maturity to close that game down. If we are in that same situation on Saturday, we're able to be smart and accurate enough to be able to shut the game down," added Gatland, who guided Wales to the semifinals of the 2011 World Cup in New Zealand, where a loss to France in the last four was followed by a defeat by Australia in the third-place play-off.
Gatland, asked if the pressure was off both Wales and Australia on Saturday, replied: "Not really. It is a little bit as we are through to the quarterfinals which means not having to desperately win the game to make the quarterfinals."
However, he added: "We're desperate to win and get a second seed team in the quarterfinal."
The Wallabies have been forced into two changes with Rob Horne (shoulder) and Michael Hooper (suspension) ruled out for the match.
Australia have made a couple changes for this clash with Sean McMahon of the Rebels cracking the nod and starts on the blindside flank in place of Hooper. Veteran Drew Mitchell comes onto the wing for Horne, after a two try performance against Uruguay earlier in the tournament made him the third highest try scorer in World Cup history.
Dean Mumm has also been included in the Wallabies run on team for the second time at the World Cup, pairing up with Kane Douglas at lock with Rob Simmons moving to the bench.
There was a injury cloud hanging over star fullback Israel Folau after suffering an ankle injury, but he has recovered for this match and starts in the number 15 jersey. Coach Michael Cheika allowed Folau extra time to prove his fitness for this match.
Prop Scott Sio, coming off his fantastic scrummaging effort against the English, starts again for Australia meaning he is the only player that has played every test for the Wallabies in the World Cup this year.
The Australians have beaten Wales in their last 10 meetings,Cheika's one win over them saw the Wallabies edge it 33-28 last November but many have been close affairs.
Cheika, who has turned the Wallabies round in under a year since replacing Ewen McKenzie, said he didn't believe they had built up momentum because of their sparkling 33-13 thrashing of England which saw the hosts consigned to the ignominy of being the first to fail to make the knockout stages.
Asked about the Welsh, Cheika said, "It's going to be another huge test match. Previous ones (matches) have been very very close. I know how hard the challenge is mentally as well as physically."
Wales, again have had to shuffle their depleted team around forcing coach Warren Gatland to make six changes from the side that beat England earlier in the tournament.
Most notably the inclusion of utility back Gareth Anscombe could prove to be a telling factor. Anscombe will start the match in the fullback position and forms part of a new look back three for this clash with Alex Cuthbert and Liam Williams on the left and right wing.
The Australians should have a good idea of what Gareth Anscombe is all about, having played for the Blues and also the Chiefs (just last year) in Super Rugby.
Paul James returns from injury to start in the front row alongside hooker Scott Baldwin and prop Samson Lee.Luke Charteris comes into the starting line up to partner Alun Wyn Jones
Ken Owens, Aaron Jarvis and Tomas Francis are named as the front row replacements with Jake Ball and Ross Moriarty completing the forward contingent. Lloyd Williams, Rhys Priestland and James Hook provide the backline cover from the bench.
Speaking about the match coach Warren Gatland said: "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 knockout phases."
Players to Watch:
For Australia: Israel Folau has had an extremely quiet World Cup so far. If the fullback can find his unplayable form he showed for the Waratahs in Super Rugby then Wales will be in for a long afternoon. David Pocock has been an absolute machine for the Wallabies so far in the World Cup. The man has one hell of a work rate. Upfront the Wallabies have really impressed, the front row of Scott Sio, veteran Stephen Moore and Sekope Kepu have truly eliminated the tag of the previous Wallabies weak scrum. Wales have been poor in the scrums so far and the Wallabies will look to dominate this area.
For Wales: Flyhalf Dan Biggar will have to be on song with the boot in this clash if Wales are to stand any chance at all. The flyhalf has been great so far, this will need to continue come Saturday. Centre George North will need to bring his "A" game for Wales this weekend. The centre is a world class player but he has been slightly quiet so far in the tournament.
Head to Head: It all starts up front, both teams have exciting backline players and both packs will be looking to get the upper hand to allow their flair players such as Israel Folau and George North some decent attacking opportunities. More low key , the battle at the lineout between Dean Mumm and Alun Wyn Jones should also be a decent contest. The biggest battle of the day (in my view) is between the two flyhalves, Bernard Foley had a great game against England , the same for Dan Biggar. Both flyhalves have had fantastic World Cups so far , this battle should be one to favor!.
Prediction: Player for player Australia possess too much class for the Welsh. I predict that Australia will win by 14 points.
