Giant winger Alesana Tuilagi collected a hat trick among Samoa's six tries in a runaway 49-12 win over Namibia to open its campaign, but it was Canada's seesawing 25-20 victory to inflict Tonga's second loss in five days that provided the event with its most thrilling result so far.
After leading 10-0, Canada conceded 20 of the next 23 points before scoring two late tries to improve to 3-0 against Tonga in World Cup head-to-heads that stretch back to the inaugural 1987 tournament, also staged in New Zealand.
Having lost to New Zealand in Friday's tournament opener, Tonga's hopes of reaching the quarterfinals for the first time look to be over.
Canada has to regroup quickly to play France on Sunday.
"That was awesome," Canada captain Pat Riordan said. "I'm so proud of the boys and the way they played and the guts they showed. We knew it was a pretty strong wind there in the second half. It just shows what the Canadian boys can do."
Apart from Tuilagi's triple, Samoa scored the first try after just 49 seconds through Kahn Fotuali'i and added another to Paul Williams, while the pack was rewarded for its relentless effort with a penalty try against a six-man Namibia scrum.
"I was pretty happy with the way the boys played today. We've still got a lot of rugby to improve, so we're looking forward to Wales," Samoa captain Mahonri Schwalger said.
But Samoa has only four days before its Pool D clash with Wales in Hamilton, and from the same side which shocked Australia in July it's likely to be without flyhalf Tusi Pisi (hamstring) and flanker Taiasina Tuifua (ribs).
Scotland won its second match in chilly Invercargill, beating Georgia 15-6 in a dour clash featuring few highlights and zero tries.
Scotland flyhalf Dan Parks kicked four penalties and a dropped goal to two penalties from opposite number Merab Kvirikashvili after the rain and swirling wind had mostly abated, making conditions more pleasant for the 10,267 fans in attendance in New Zealand's southernmost city.
A day after losing lock Courtney Lawes to a two-match suspension, England's bid to reach back-to-back World Cup finals received another blow with destructive scrummager Andrew Sheridan's troublesome left shoulder ending his involvement at the tournament.
The 1.95-meter and 125-kilogram loosehead prop was instrumental in dismantling Australia's scrum at the 2007 quarterfinals and helping England progress to a final it ultimately lost to South Africa.
England team manager Martin Johnson is yet to select a replacement for Sheridan, who has had two operations on his left shoulder and one on his right.
"It's really sad for Sheri," Johnson said. "He has been unlucky with injuries."
Another player returning home is France's David Skrela. The backup flyhalf, who has also undergone surgery on both shoulders, was hurt in the team's unimpressive opening Pool A win against Japan on Saturday.
France coach Marc Lievremont's belated decision to replace Skrela means his next choice, untested utility half Jean-Marc Doussain, is unlikely to be available for action until the final pool match against Tonga on Oct. 1.
It's the latest curious move by Lievremont, whose public tirade on Sunday against his players for their form against Japan upset scrumhalf Dimitri Yachvili, indicating that the schism that emerged after he called them cowards following a Six Nations loss to Italy hasn't totally healed.
"I hope we don't have any more injuries against Canada because it will be difficult for him to be on the teamsheet," Lievremont said of Doussain. "Give him time to get over his jet lag and settle in with us, otherwise we'll have to rush things."
The French won't be rushing anything on Thursday, the players opting for more soothing activities on their day off than the white water rafting, jetboat skiing and bungee-jumping that the England camp took part in on Monday.
"I would rather go for a walk, make the most of the good weather," Imanol Harinordoquy said, while teammate Jean-Baptiste Poux added of bungee-jumping: "It must stir the emotions up. I'm not sure if I would enjoy it ... I think some would have vertigo and wouldn't be able to do it."
The only match on Thursday is a Cold War classic with the United States going up against Russia at Stadium Taranaki in New Plymouth.