BRAMPTON, ONTARIO -- It was career goal No. 67 for Natalie Spooner in Canadian colours, but her first as a mom.

The 32-year-old forward, who gave birth to son Rory on Dec. 6, wasted little time getting back on track Wednesday in Canada's comfortable 4-0 win over Switzerland in its opening game at the IIHF Women's World Hockey Championship.

Spooner, competing in her ninth world championship, gave Canada a 1-0 lead at 11:42 of the first period, beating goalie Andrea Braendli with a wrist shot after the Swiss defence failed to clear a puck.

"It was awesome," said Spooner. "Just to get back out there even with my teammates, I was having a blast."

"It's pretty amazing how supportive my teammates and Hockey Canada have been with this whole thing,' she added. "And obviously it's a lot for me to juggle. But I mean he's got so many aunties around. They hold him at meals and make sure he's happy so I can eat. My mum is also here helping...He's been pretty happy around the girls, which is great. He loves them."

Rory has become a favourite with the entire Canadian contingent, according to Canada coach Troy Ryan.

"It's actually been a lot of fun for our team, the athletes and our staff, just having little Rory around with us everywhere we go," he said.

"My hat is off to her," added Canada captain Marie-Philip Poulin. "It's amazing. You could see the reaction on the bench, how happy we were for her."

Sarah Nurse, Rebecca Johnston and Sarah Fillier also scored for Canada in a game that had flashes of ill-temper, especially in the second period. The Canadians outshot the Swiss 49-12, including 25-1 in the third.

Johnston also took a break from hockey last fall, to nurse a back injury.

The defending champion Canadians, who have never missed a worlds podium, are looking for a 13th world title. The Swiss, who won bronze in 2012, are hoping to improve on fourth-place finishes at the last two tournaments.

Attendance at the CAA Centre, whose capacity is listed at 5,000, was announced at 3,510. Most of those in the stands were wearing red.

"We felt the energy obviously from the crowd," said Poulin.

Canada came out flying but soon found itself on the back foot, having to kill off three early penalties including a 65-second sequence when it was down two players.

The penalties killed, Nurse then made the Swiss pay for taking a high-sticking penalty, scoring from the slot just 15 seconds into the power play at 14:27 to make it 2-0.

Canada struck again on the power play at 1:44 of the second with Johnston facing a gaping goal with Braendli out of position after making a stop on Jamie Lee Rattray.

Ryan complimented his squad's special teams on the night, but said there were some details that needed to be ironed out.

The Swiss thought they had scored midway through the period but the puck somehow stayed out, with Canada going a woman down after the scrum that ensued. A Swiss player went off soon after as the game turned physical.

After being outshot 9-8 in the first, Canada had a 16-2 advantage in the second and fired 11 shots in the third before the Swiss managed their first of the period.

Fillier made it 4-0 with Canada's 19th shot of the period, slotting the puck home from in close at 14:07.

Canadian goaltender Ann-Renee Desbiens got the shutout.

In the earlier Group A game Wednesday, the U.S. defeated Japan 7-1. That meant listening to Smash Mouth's cover of the Monkees' "I'm a Believer" seven times during the goal celebrations.

Haruka Toko opened the scoring at 8:14, giving the underdog Japanese cause for celebrations.

"It was a crazy atmosphere on the bench. We were just so happy for each other and the program and how far we've come," said forward Chihiro Suzuki, who plays for the University of Guelph.

Born in Japan, the 20-year-old has spent the last nine years in Canada to pursue hockey.

The Americans rallied to lead 2-1 at the end of a first period that saw them fire 23 shots at five-foot-two goaltender Miyuu Masuhara compared to just five shots for Japan. Masuhara gave way to 18-year-old Riko Kawaguchi midway through the second period with the U.S. leading 4-1.

It was a gritty showing by Japan which finished a career-best fifth at last year's worlds by edging Sweden in a shootout.

The Japanese, outshot 59-13, were outmatched when it came to size but not in resolve.

The average size of Japan's roster is five foot four and 130 pounds compared to 5-7 and 152 pounds for the Americans whose captain, Hilary Knight, at five foot 11 and 172 pounds, is 13 inches taller and 57 pounds heavier than Japanese forward Remi Koyama.

"They don't back off...They are going to give you everything they have. It showed by them getting on the (score)board first," U.S. coach John Wroblewski said of Japan. "It was something we were going to have to scratch and claw to get back to. I liked how we got our legs underneath us and we applied some of the things, the plans we wanted to play with.

"I thought up and down our lineup we had strong performances."

The tournament opened Wednesday with nine different Finns scoring in a 14-1 win over France in Group B play. Jenniina Nyland recorded a hat trick as Finland peppered goaltender Caroline Lambert in outshooting France 53-12.

It marked the most goals Finland has ever scored in a game, beating its previous mark of 13 against Switzerland in both 1992 and 1994. Finnish captain Jenni Hiirikoski has now played in 83 games at 15 world championships.

The Swiss were led by star forward Alina Mueller, who suffered a tournament-ending ankle injury at the 2021 worlds in Calgary and came down with COVID during last year's tournament in Denmark.

A finalist for the Patty Kazmaier Memorial Award which goes to the female NCAA hockey player, the 25-year-old Mueller has 27 goals and 33 assists in 38 games for Northeastern this season.

Canada defeated Switzerland 12-1 in group play and 10-3 in the semifinals at the 2022 Beijing Olympics. The Canadian women went on to beat the U.S. 3-2 to claim gold while the Swiss lost 4-0 to Finland in the bronze-medal game.

Canada also beat Switzerland 8-1 in the semifinals of the 2022 world championship.

The Canadians face 2022 worlds bronze medallist Czechia on Friday.