Defenceman Axel Sandin Pellikka scored a natural hat trick as Sweden kicked off the tournament with a 5-2 rout of Slovakia.
Sandin Pellikka, a Detroit Red Wings prospect playing in his third world juniors, added an assist for Sweden, which is looking for its first title since 2012.
Rasmus Bergqvist and Linus Eriksson had the other goals for Sweden.
Dalibor Dvorsky had a goal just under 12 minutes into the game to open the scoring for Slovakia, which was then held without a goal until Daniel Jencko scored on a power play with 85 seconds left in regulation.
Sweden plays Kazakhstan and Slovakia meets Switzerland on Friday.
In other games Thursday, Czechia played Switzerland and host Canada took on Finland.
