Wales produced "half a performance" to beat Canada 42-17 in their Pool B match at Stade La Beaujoire in Nantes on Sunday.
Wales finished with five tries but only after Canada ran in three and controlled the match until the 52nd minute, quietening the Welsh fans who accounted for more than half the 38,000 capacity of the stadium.
Wales made two critical replacements in the second half, bringing on fly half Stephen Jones and squad captain Gareth Thomas for his 98th Test.
Head coach Gareth Jenkins was happy to come away with the win but said he was "disappointed" at half time.
"Canada had a part to play in that and give them credit, really, for putting us up to the sword, putting a lot of pressure on us and making it a difficult 40 minutes of rugby that we had to play against."
However, he was pleased with one aspect of the match.
"What I was positive about, really, was our reaction after conceding a try in the second half as well."
Wales led 9-0 after 20 minutes but the first half belonged to the Canucks with the superior territory advantage and two magnificent tries.
Canada head coach Ric Suggitt was excited about the half-time score.
"I wished it would have ended at half time," he said.
"It surely shows that with the right preparation we can compete against the top teams in the world and Wales is one of those teams.
"We're not shy about what we want to achieve and we'll keep backing ourselves no matter what all the critics say or all the naysayers say about the segregation of rugby. They can stuff themselves!"
It was the injection of Stephen Jones (WAL) just after half time that turned the tide for Wales.
The presence of the fly half brought a new-found confidence and energy to his side.
"Stephen's got great experience, where we were lucky today was we had a strong bench and they definitely affected and made an impact," said Jenkins.
"Sometimes you need to makes changes - that's what the team's about."
Jones completed the scoring for Wales, kicking his fourth conversion from five attempts.
Wales will take the second half confidence into a clash against Australia for what may be the pool decider at Cardiff's Millennium Stadium on Saturday, 15 September.
Canada will have gained plenty of confidence for the clash with Fiji in Cardiff the following day.