Australia and Wales face off at Twickenham for the right to top Pool A.
In the first of the three Saturday games, Scotland need three points against Samoa in Newcastle to secure the runners-up spot in Pool B and be the first of the Six Nations sides to know their exact place in the knockout draw.
Japan's shock success over South Africa on the first Saturday of the tournament has meant that anything less than victory or a draw with a bonus point for Vern Cotter's team, and the Brave Blossoms have a chance of nicking the berth behind South Africa. A simple draw for Scotland and Japan will need a try-bonus victory over the USA on Sunday to claim second spot, a defeat to Samoa, like on their last meeting two years ago, and the Brave Blossoms just need to beat the Eagles.
However, Vern Cotters smart selection against South Africa has meant his best team come into this game fighting fit and they will be ready to give it there all come kick off. The shining light of Scottish football at the minute is Fly Half Finn Russell, he gives this Scottish back line a sharp positive edge, something it has lacked for many years.
Samoa have been disappointing to date in this World Cup and on the face of it they have nothing to play for, but should they get try-bonus win and Japan lose and can claim third place.
Expect this game to tight and the boot of Greig Ladlaw to be the difference. Samoan indiscipline will be punished and if Scotland accumulate a lead this will increase the pressure on Samoa.
Australia were awesome under pressure against England at Twickenham last Saturday, and have beaten Wales on each of their last ten meetings.
But the Dragons are the bet with a start of eight points on the handicap in this Pool A top-spot decider at Twickenham this afternoon.
Only one of the last eight of these defeats has been by nine points or more and Wales were brave beyond belief in pulling off their heist against the Red Rose a fortnight ago.
Also Wales may have had to contend with more disruption than the Wallabies before the tournament began and in the early weeks, but theirs has been a smoother build-up this week.
Wily head coach Warren Gatland, who masterminded a British & Irish Lions Test tour success down under two years ago and presided over Wales' last win over the Wallabies seven years ago too, seems to have come up with a multi-faceted plan to try and pinch victory as well.
Two opensides in skipper Sam Warburton and Justin Tipuric have been picked to try and boss the breakdown with Aussie ace Michael Hooper banned.
Two heavyweight, straight-running centres in Jamie Roberts and George North have been picked to try and run down Aussie inside centre Matt Giteau, an injury doubt earlier in the week, and drag across Bernard Foley and Tevita Kuridrani and distract all three from attacking duties.
In the front-five, Gatland has picked Alun-Wyn Jones and Luke Charteris at lock and Paul James and Samson Lee as props for the set-piece battles.
Jones skippered the Lions to victory in the third Test after injury ruled out Warburton and he and Charteris were the starting second-rows in November 2008 when Wales last beat Australia.
James and Lee are not back-up boys by any stretch of the imagination and Gatland has thrown down the gauntlet to them to prove that they are over their fitness troubles and ready for the knockout stages.
It is a similar test for Gareth Anscombe at full-back, who has won Super Rugby titles with the Chiefs but only came up to Cardiff from New Zealand last year and qualifies through a Welsh mother.
Gatland's plans may not work but at least Wales are not treading water with their tactics, which may be the case with the Australians even if the urge to avoid a quarter-final with South Africa rules out complacency.
Wales have been forewarned about Foley's running from fly-half and his use of close runners, while surely the Wallabies will be reticent about flagging up for future opponents new backline tricks.
Wales and Australia have both scored over 50 points against Uruguay and Fiji would have too at Milton Keynes on Tuesday if it had not been for the rain, so England should run riot in Manchester this evening.
General dismay at being eliminated and the all-sorts nature of Stuart Lancaster's team selection means no handicap bets appeal. However, two odds-against England tryscorers do. They are number eight Nick Easter at 6-4 and replacement hooker Jamie George at 4-1. Both men will get involved in England rolling mauls and forward-orientated moves and they also possess the handling skills and running lines to be effective if finding themselves in phase play out in the backs. Easter has six tries in 53 Tests and may switch to lock and play the full 80 minutes while rookie George has proved he knows where the tryline is in club rugby for Saracens.