Wales will be hoping for a victory over Australia which will put them in pole position to finish top of Pool D and potentially secure a more favourable route in the knockout phase.
Matches against England and New Zealand, though, could be on the horizon for the losers, which underlines the huge stakes in what could be the game of the tournament so far.
Elsewhere, Uruguay will be looking to replicate their superb performance against Fiji when they face Georgia in the other match in the pool.
Williams lauds Wyn Jones
Liam Williams hailed Alun Wyn Jones' "incredible" achievement as he prepares to break Wales' international appearance record.
Wales captain Jones will win his 130th cap when he leads the team against Australia at Tokyo Stadium.
Only New Zealand's World Cup-winning captain Richie McCaw, former Ireland centre Brian O'Driscoll and Italy skipper Sergio Parisse will have played in more Tests than Jones after this weekend.
"It's incredible," Wales full-back Williams said. "I read something online that he has been playing for Wales for 13 years.
"I have been here for seven years and feel like I've been here for ages, and it's almost double me!
"He is a great bloke and leads from the front. He speaks well, and does his talking on the pitch as well. He is a leader, and I'm sure it will be a great occasion for him on Sunday."
Cheika: History has no impact
Australia coach Michael Cheika believes history will have no relevance when his side run out to face Wales.
Wales ended Australia's long run of success in the fixture by beating them last November.
That win was part of a record 14-Test unbeaten sequence which also helped Wales briefly become world rugby's number one-ranked team but Cheika insists it will be back to square one on Sunday morning.
"I think every match in the World Cup is a grand final. Whether you can try to isolate one more than the other, I personally don't believe so.
"All that history stuff between one team and another doesn't count because you get out there and it is zero-zero.
"I've been privileged to be a part of a few of these (Wales versus Australia games) now. It was my first ever Test match in charge of Australia.
"We like to run with the ball. They like a lot of counter-attack footy sometimes, and they are great defenders as well.
"We've got very contrasting styles. One thing you see in these games is full commitment from all players on both sides, and that is what usually makes them pretty tight."
Japan shock the world – again
Hosts Japan rocked the globe for the second time in four years on Saturday by stunning Ireland 19-12 in their Pool A clash in Shizuoka.
The Brave Blossoms tore through Ireland time and time again, triumphing through superior tenacity and supreme intensity.
Wing Kenki Fukuoka ran in the second-half try which sealed Japan's famous victory – invoking memories of their breathless 34-32 win over South Africa in Brighton at the 2015 World Cup.
Elsewhere, South Africa shrugged off defeat by New Zealand in their opening match to sweep past neighbours Namibia 57-3 at the City of Toyota Stadium.
Rassie Erasmus' men – captained by veteran Schalk Brits playing at number eight – dominated from the off against the lowest-ranked team at the World Cup.
Hooker Bongi Mbonambi powered over for two tries, with wing Makazole Mapimpi also claiming a brace, while Elton Jantjies booted six conversions as the Springboks made sure of both a convincing victory margin and perhaps a crucial bonus point.
Also on Saturday, Argentina hooker Julian Montoya scored a hat-trick as the Pumas recovered from their narrow defeat to France to beat Tonga 28-12 in Osaka.
Uruguay ready for repeat
Uruguay back rower Juan Diego Ormaechea insists the South Americans are determined to produce another World Cup shock against Georgia.
Fiji were stunned in Pool D on Wednesday when Uruguay achieved the greatest result in their rugby history with a 30-27 victory in Kamaishi.
"We're still happy but we know it's in the past," Ormaechea said of the Fiji win ahead of the Georgia clash in Kumagaya.
"We're very focused on this game. We knew we would have only three or four days (turnaround) and we are 100 per cent focused on Georgia.
"It's a game that will demand that kind of energy and mental focus again."
Stat attack
Alun Wyn Jones will become Wales' most-capped player when he runs out for the 130th time in his nation's colours.
