George Gregan v Gareth Cooper
If Cooper gets the nod at scrum-half he will be in for one of the sternest tests of his career when he comes up against the most capped scrum-half in rugby history - with 83 - and rated as probably the finest all-round No 9 in the world.
The 30-year-old Gregan has been a mainstay in the Australia side and has missed just nine Tests since making his international debut against Italy in 1994 - forming a lethal partnership with ACT Brumbies teammate Stephen Larkham
A fierce competitor and tenacious defender, Gregan was the natural successor to World Cup-winning skipper John Eales, having already served as vice-captain, and was voted International Players' Association World Player of the Year in 2001.
Cooper, meanwhile, has been hindered from staking a full-time claim to the Wales No 9 jersey, that he was expected to inherit from Rob Howley, by a catalogue of injuries that have restricted him to just seven caps.
The 24-year-old Pencoed product has, however, already been singled out by Wallaby coach Eddie Jones as a future star having also impressed in the Zurich Premiership with Bath.
David Giffin v Robert Sidoli
Sidoli has been a Test regular for Wales since making his debut out in South Africa a year ago and has already set about stamping his authority in the Welsh lienout.
But he will be in for a stern test should he keep his place on Saturday against one of the most well respected second-rows on the international arena.
This year's Super 12 season has seen Giffin return to his previous best having missed almost the whole of 2002 through a shoulder injury. Despite that injury, Giffin, who learned his trade alongside Wallaby legend John Eales, had been noted for his durability and played 25 consecutive Tests before injury against the British Lions in 2001 ended that run.
Sidoli, six years younger than Giffin, has made a big impression in his 10 appearances for Wales having earned his promotion to the national side as part of the young Pontypridd pack that proved so destructive both at home and in Europe last season.
Elton Flatley v Stephen Jones
Flatley emerged from the shadow of Stephen Larkham with an outstanding two-try performance against England at Twickenham last November and was again at his inspirational best against Ireland last Saturday.
The Queensland Reds outside-half scored a virtuoso solo effort at a crucial moment when he stepped inside two defenders before rounding Peter Stringer to score under the posts just a minute after Ireland had taken the lead.
But he also proved what a strong defender he as well with a stunning try-saving tackle on Girvan Dempsey just yards from his own goal line later in the game. There are question marks over his tactical kicking perhaps, but deadlywith the ball in his hand.
Jones has been the mainstay of Llanelli's European success in recent seasons, he is the man in possession of the Wales No10 shirt and he will probably Wales' most important player this Saturday.
If he can keep the Wallabies pegged back in their territory, and convert any penalty chances that come his way, the underdogs will be in with a shout.