Stand-in captain France captain Yannick Bru blamed the wind for his side's mixed performance against the USA.
Bru believes France will get better yet
The French ended the match comfortable winners but failed to really convince, having led the game in Wollongong 26-0 at half-time.
And Bru said: "After a good first half our legs were very, very heavy. It was not easy because of the wind tonight.
"And most of the players who were at the game today are not used to playing."
South African-born centre Brian Liebenberg was the star for France with ball in hand, scoring a hat-trick in his first World Cup start.
Bru himself and Jean-Baptiste Poux added his side's other tries to ensure a maximum 20 points from their four Pool B games.
And the temporary skipper, who looks set to lose his place to Raphael Ibanez at hooker for the quarter-finals, is confident sides can expect more from France in the knock-out stages.
Bru said: "I think we are coming better physically and technically. Everything is better and better Saturday after Saturday."
However he insisted he would keep a close eye on the Pool A match between Ireland and Australia. The runner-up faces France in the quarter-finals.
"We hope that it will not be a big surprise and the Wallabies will beat Ireland because I think it would be very hard to beat the Wallabies at home," added Bru.