Australia coach Robbie Deans has been forced into naming number eight Radike Samo on the wing for the Pool C clash against Russia on Saturday.
Deans has named the 35-year-old forward out of position for the match in Nelson as his squad has been ravaged by injury.
Utility back Pat McCabe (shoulder), full-back Kurtley Beale (hamstring), winger Digby Ioane (broken thumb), and centres Rob Horne (broken cheek) and Anthony Faingaa (concussion) are all unavailable for Australia's final pool game.
Samo, who scored a try from the wing in the victory over the United States, showed his pace with a stunning 65m try in the Tri-Nations victory over New Zealand in August, outsprinting wing Cory Jane and full-back Mils Muliaina to score.
He becomes the first player to start as a forward and a back in the same World Cup.
"It's a position he's familiar with," said Deans. "He started on the wing and as recently as last weekend you saw him there.
"He's a remarkable athlete. He's 35, I understand, and he can still run really fast."
There are a total of nine changes to the side that beat the USA, as Deans has also had to deal with the loss of loose forward Wycliff Palu, who is out of the tournament with a hamstring injury.
The impressive Berrick Barnes teams up with Adam Ashley-Cooper in midfield, while James O'Connor moves to full-back.
Influential open-side flanker David Pocock returns from injury, as does skipper James Horwill, who missed the USA contest to rest a shoulder problem.
Ben McCalman moves to number eight while Scott Higginbotham starts on the blind-side flank.
Hooker Stephen Moore and prop Sekope Kepu come into the front row.
With resources scarce, Deans has had to name two hookers, Tatafu Polota-Nau and Saia Faingaa, along with scrum-halves Will Genia and Nick Phipps on a lop-sided bench.
"We've had to be a bit creative but it's never been about the number on their back," added Deans.
"While some of them might be out of their normal positions, they won't let us down and will enjoy the opportunity."
Australia are expected to finish second in the group following the defeat by Ireland, and are likely to play South Africa in the last eight.
Australia team: 15-James O'Connor, 14-Radike Samo, 13-Adam Ashley-Cooper, 12-Berrick Barnes, 11-Drew Mitchell, 10-Quade Cooper, 9-Luke Burgess, 8-Ben McCalman, 7-David Pocock, 6-Scott Higginbotham, 5-Nathan Sharpe, 4-James Horwill (captain), 3-Sekope Kepu, 2- Stephen Moore, 1-James Slipper.
Replacements: 16-Tatafu Polota Nau, 17-Saia Fainga'a, 18-Salesi Ma'afu, 19-Rob Simmons, 20-Rocky Elsom, 21-Will Genia, 22-Nick Phipps.