Gontineac - big task for his team (Getty Images).

By Simon Stone, PA Sport, Sydney

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Romanian skipper Romeo Gontineac has admitted his team must get their heads sorted if they are to stand any chance of shocking Argentina at Aussie Stadium on Wednesday.

After putting up a creditable display in their opening game against Ireland, Romania found themselves badly outgunned by Australia at the weekend.

The outcome was a 90-6 defeat, the biggest hammering in a series of lop-sided contests so far, and Gontineac acknowledged the mental scars still remain.

"The loss against Australia was so big it will be difficult to get ourselves mentally right for another match in such a short space of time," said the Aurillac centre.

"The Wallabies were under pressure to do well because they were not too convincing in their first match and with over 50,000 supporters cheering them on as well, it turned into a very hard game for us."

The challenges are not getting much easier either with Argentina desperate to record a big win to give them a confidence lift ahead of Sunday's crucial clash with Ireland in Adelaide which will determine who advances into the last eight along with Australia.

Pumas coach Marcelo Loffreda has made six changes to the second string side that beat Namibia last week, with flanker Santiago Phelan becoming the third different player to captain the team in as many games.

Significantly, Mario Ledesma, who under-performed badly in the tournament opener against Australia, is named as hooker, suggesting former Northampton front-row Federico Mendez is being held back to face the Irish.

Like Mendez, experienced half-back duo Agustin Pichot and Gonzalo Quesada have been allocated bench spots just in case the game does not go as Loffreda plans.

The Pumas boast a 100% record in their six encounters with Romania, although the pair have not met since 1998 when Argentina scored nine tries in a 68-22 romp.

Romania's leading try-scorer Gabriel Brezoianu switches to full-back from his usual wing berth as Danut Dumbrava misses out with a shoulder injury, while flanker Marian Tudori and wingers Ioan Teodorescu and Mihai Vioreanu are introduced for the first time.