Wales (9) 42
Wales finally won enough ball to allow their backs to show their class
Tries: Parker, AW Jones, Williams (2), Charvis
Cons: Jones (4)
Pens: Hook (3)
Canada (12) 17
Tries: Cudmore, Culpan, Williams
Wales survived a huge scare in their opening World Cup match before overcoming a determined Canada side.
Canada led 17-9 after 45 minutes in Nantes after tries from Jamie Cudmore, Craig Culpan and Morgan Williams.
But the introduction of Stephen Jones and Gareth Thomas sparked Wales to life as they dominated the last half hour.
Sonny Parker, Alun Wyn Jones, Colin Charvis and Shane Williams (2) crossed to ensure the victory which had looked a distant dream for the Welsh side.
Wales, wearing black armbands in honour of former Welsh Rugby Union president Sir Tasker Watkins who died on Sunday, lined up in unfamiliar grey jerseys.
And the dullness of their shirts was matched by their play in the opening exchanges as they struggled to find any cohesion.
They at least managed to force Canada to concede penalties in their own half, and James Hook kicked three of his four attempts to put Wales 9-0 up after 15 minutes.
Canada's intentions were clear after picking a strong and experienced pack, and their opening try on 25 minutes all down to forward power.
A scrum deep in Wales 22 provided the perfect attacking platform, and Cudmore eventually barged his way over from a few yards out as Wales buckled under heavy pressure.
Wales were left stunned 10 minutes later as Culpan ran almost the length of the field to score Canada's second try.
Wales had looked destined to score as a break by centre Tom Shanklin put Canada on the back foot, but Hook's attempted long pass was intercepted by Culpan and the centre had enough pace to race home.
Pritchard converted and the half-time whistle came as a blessing for the shell-shocked Wales players.
The break had little effect, though, as Canada scored their third try after just five minutes of the second-half.
Scrum-half Williams made the initial break before the Canada forwards again inched their way towards the Wales line with powerful drives.
Shanklin was Wales' most potent attacking threat in Nantes
The score looked inevitable, and it was Williams who finally borrowed his way through.
Wales needed a quick response, and coach Gareth Jenkins immediately turned to the experience of Thomas and Stephen Jones
The change had the desired effect as Wales finally came alive.
Jones almost scored with his first touch, a desperate Canadian covering tackle preventing the fly-half from grounding the ball as he dived over the tryline.
But the crucial score arrived moments later from the resulting scrum as Jones' reverse pass sent Parker over. Jones converted to bring Wales back to within a point.
Wales finally had the initiative, and they regained the lead five minutes later.
A Canada clearance from behind their own tryline was charged down and lock Alun Wyn Jones pounced on the loose ball to score.
With the Canadians tiring, the outstanding Shanklin then had a hand in the next two Wales tries as Williams crossed twice in as many minutes.
A Stephen Jones break then laid a try on a plate for flanker Charvis, another replacement who played a huge part in Wales' revival.
Jenkins had stressed the importance of starting their campaign with a win, but Wales will need to raise their game a few notches if they hope to challenge Australia in next Saturday's crucial group match in Cardiff.
Wales: Morgan; M Jones, Shanklin, Parker, S Williams; Hook, Peel (capt); G Jenkins, M Rees, A Jones, Gough, AW Jones, J Thomas, M Williams, Popham.
Replacements: T Rhys Thomas, D Jones, Owen, Charvis, Phillips, S Jones, G Thomas.
Canada: Pyke; Van der Merwe, Culpan, Spicer, Pritchard; Monro, Williams (capt); Snow, Riordan, Thiel, Tait, James, Cudmore, Biddle, Stephen.
Replacements: Carpenter, D Pletch, M Pletch, Burak, Yukes, Fairhurst, Smith.
Referee: A Rolland (Ireland)