Clayton Keller scored twice and the United States overcame a slow start to beat Latvia 6-1 at the world junior hockey championship on Monday.
Patrick Harper opened the scoring for the Americans 6:27 into the game, but Renars Krastenbergs responded for Latvia to make it 1-1 after the first period in the tournament opener for both teams at Toronto's Air Canada Centre.
The U.S. regained the lead when Colin White scored 6:29 into the second and Keller made it 3-1 late in the period.
''We got better as the game went on,'' U.S. coach Bob Motzko said.
''You could tell there were some nerves in the first period, but after the guys settled in we found our style of play and got the job done. We'll learn from this as we get ready for the next one.''
Keller scored his second of the game with 7:41 to play in the third. Jeremy Bracco added another at 17:31 while Jordan Greenway got on the scoreboard in the final minute.
Troy Terry and Tage Thompson each added two assists for the U.S.
U.S. goalie Tyler Parsons only had to make 11 saves for the victory. Marek Mitens stopped 24 of 30 shots for Latvia.
The U.S. next faces Slovakia on Wednesday.
Later in Toronto, Canada scored three power-play goals, including a pair by captain Dylan Strome, to open the tournament with a 5-3 victory over Russia.
It was a strong start against a tough opponent for Canada, which has been shut out of the medals at three of the past four world juniors. The Canadians dropped their tournament-opening game to the Americans last year before finishing sixth in Finland in their worst showing in almost 20 years.
Tyson Jost, Nicolas Roy and Matt Barzal also found the back of the net for the Canadians, and Carter Hart yielded three goals on 17 shots.
In Montreal, Michael Spacek scored with 1:18 left to lift the Czech Republic to a 2-1 victory over defending champion Finland.
Spacek, a Winnipeg Jets prospect with the Western Hockey League's Red Deer Rebels, fired a shot through traffic from just inside the blue line that went inside the post.
Daniel Krenzelok also scored for the Czechs, who are seeking their first world junior medal since they took bronze in 2005.
Joona Luoto scored for Finland, which has won two of the past three world juniors including last year at home.
Earlier in Montreal, Alexander Nylander scored twice and 16-year-old Rasmus Dahlia had a goal and an assist and Sweden routed Denmark 6-1.
Carl Grundstrom, Joel Eriksson Eke and Jonathan Daylen also scored for Sweden, seeking its first world under-20 gold since 2012 in Calgary and Edmonton.
Dahlia, a defenseman in Sweden's top league, is seen as a potential No. 1 overall NHL draft pick in 2018 and has been compared to Ottawa Senators star Erik Carlson.
Nikolay Crag scored with 2:07 remaining for Denmark on a screened shot from the left circle to spoil Felix Sandstorm's shutout bid.
Nylander, drafted eighth overall by Buffalo in June, picked up a puck from Filip Hal, made a move in the slot and slid it past Petersen at 10:11 of the first to open the scoring.