The U.S. scored every time a Canadian was in the penalty box in the opening period of Saturday's game. Three power-play goals were the difference in the Americans' 4-2 victory to open the tournament.
Both countries play their second Pool A game in as many days Sunday when Canada takes on Russia and the defending champion U.S. meets Finland.
Jocelyne Lamoureux, Kacey Bellamy and Kendall Coyne scored for the U.S. in the first period and Hilary Knight even-strength in the third. Brianne Jenner of Oakville, Ont., and Jennifer Wakefield of Pickering, Ont., countered for Canada.
Genevieve Lacasse of Kingston, Ont., made 30 saves in the loss. She was scored on by her CWHL Boston Blades teammates Bellamy and Knight.
Lacasse was pulled for an extra attacker with over two minutes to go in regulation, but the reigning Olympic champions did not score again.
The Canadians were more organized in the second and third periods. Wakefield pulled them within a goal in the first minute of the second Canada killed off a pair of U.S. power plays in the third.
But Knight restored her country's two-goal lead at 6:29 of the third. Canada's attack was anemic with just 11 shots on U.S. goalie Jessie Vetter.
"We came to work hard, but I don't think we were working that smart," Canadian head coach Doug Derraugh said. "We just had to believe in the systems and stick to what the game plan was and not just get running around and chasing the puck.
"Disappointed, but I think we can build off of some of the adjustments we've made."
The Americans have been lethal a player up in recent years with a 31 per cent success rate in last year's Winter Olympics. They were a combined 34 per cent over the three world championships prior to that.
So even with 10 players making their world championship debut Saturday — the same number as Canada — the Americans had their special teams in order at the opening faceoff.
They scored their first of their three power-play goals during a two-man advantage. The U.S. also held Canada scoreless on their four power-play chances.
"Every line can play on the power play. Every d-pair has been playing," Bellamy said. "It's just using each other and communicating and finding the open slots and putting pressure on the puck whenever we lose it."
Canadian captain Marie-Philip Poulin took a blast off her right leg while helping kill off a U.S. power play early in the third. She was in pain getting to the bench, but shook it off and continued to play.
"At the moment, my leg fell asleep, but it was worth it," Poulin said. "They have a great power play. They move around pretty well so we're going to watch some video and maybe tighten up on the penalty kill."
Finland edged Russia 3-2 in a shootout in Saturday's other Pool A game
Olympic bronze medallist Switzerland downed Germany 5-2 and Japan shocked host Sweden 4-3 in a shootout in the first Pool B games.
The two countries with the best records advance to the quarter-finals against the two lowest-ranked countries in Pool A. The top two countries in Canada's pool earn byes to Friday's semifinals.
A tournament format change in 2012 incorporated a preliminary-round game between the two countries that have met in the final of all previous 15 world championships.
Canada versus the U.S. provides a marquee matchup on the first day the championship, but the result hasn't been an indicator of the outcome should they again meet in the final.
Canada took its worst beating ever from the U.S. in the preliminary round of 2012, but recovered from the 9-2 debacle to prevail 5-4 in overtime for gold.
The U.S. fell 3-2 to Canada to open the 2013 championship Ottawa, but won the final and the world title 3-2.