For Italy it's just about getting through tonight's game against USA in Nelson intact, and with the win.

Then they can think about their crucial clash with Ireland.

The complicated nature of Pool C means that if Italy can beat Ireland next week they'll go through to the quarterfinal and Declan Kidney's side will go home, despite that historic win over Australia.

It is arguably the biggest game in the history of Italian rugby, but before then there is work to be done tonight.

"This match is important for two reasons," said Italy flanker Mauro Bergamasco.

"One, to keep our competition alive because we have to win to stay in contention for the final pool match. Secondly, we need to repeat our performance from our last match [against Russia] to give ourselves confidence ahead of the match with Ireland.

"The United States are very physical and have improved their game plan over the last few years and we saw that they really troubled Ireland.''

This will be USA's last World Cup game and their captain Todd Clever says there's only one way they want to bow out.

"The guys are keen and hungry," he said. "I definitely back the other 21 guys who have the jersey. It's going to be a big challenge, we all know that, but you don't go into a game thinking you can't win."

USA: Chris Wyles, Taku Ngwenya, Paul Emerick, Andrew Suniula, James Paterson, Roland Suniula, Mike Petri; Nic Johnson, Todd Clever (c), Louis Stanfill, Hayden Smith, John van der Giessen, Matekitonga Moeakiola, Chris Biller, Mike MacDonald. Reserves: Phil Thiel, Shawn Pittman, Scott LaValla, Pat Danahy, Tim Usasz, Nese Malifa, Blaine Scully.

Italy: Luke McLean, Tommaso Benvenuti, Gonzalo Canale, Gonzalo Garcia, Mirco Bergamasco, Luciano Orquera, Fabio Semenzato; Sergio Parisse (c), Mauro Bergamasco, Alessandro Zanni, Cornelius van Zyl, Quintin Geldenhuys, Martin Castrogiovanni, Leonardo Ghiraldini, Salvatore Perugini. Reserves: Fabio Ongaro, Andrea Lo Cicero, Marco Bortolami, Paul Derbyshire, Edoardo Gori, Riccardo Bocchino, Giulio Toniolatti.