Fly-half Stephen Jones bemoaned Wales' sluggish start in the 32-20 loss to Australia at the Millennium Stadium.
Jones says there is more to come from Wales in this tournament
"We weren't clever in the first half, there were a lot of errors and we weren't efficient," said Jones.
"We were confident going in, but we let them put in the big hits, slow our ball down, and turn us over.
"That changed after the break and we caused them problems. We have to learn to play for 80 minutes, there's more to come from us in this World Cup."
If Wales can secure second spot in the group, they will expect to meet likely Pool A winners South Africa in Marseille.
"The quarter-finals have always been our ambition, but we have to get to there before thinking about opposition," Wales coach Gareth Jenkins told BBC Sport Wales.
The momentum we created and the chaos we can bring to defences had Australia in some trouble in the second half
Wales coach Gareth Jenkins
"There's a quick turnaround before we play Japan on Thursday, and two huge games to come against them and Fiji."
Jenkins, who says that there will be no news of the injuries to Gareth Thomas and Sonny Parker until Sunday, believes that Wales' second-half display gives hope for the rest of the tournament.
"In the first half we gave them too much respect and too many scoring opportunities - and they were very clinical," said Jenkins.
"At half-time we knew that we were a better team than we had shown and we needed to prove that to ourselves and to other people.
"I think that we did that and emerged with an amount of credit.
"If Australia hadn't got the second try from [Chris] Latham it would have been game on.
"The momentum we created and the chaos we can bring to defences had Australia in some trouble."