The powerful United States squad defeated Latvia 5-2.
Luke Hughes, Red Savage, Chaz Lucius, Sean Behrens and Jimmy Snuggerud scored for the U.S.
Anri Ravinskis and Niks Fenenko replied for Latvia.
The teams were scoreless after the first period and tied 2-2 heading into the final frame.
Switzerland stuns Finland
Earlier in the day, Attilio Biasca scored the game-winning goal 41 seconds into overtime as Switzerland opened their tournament with a 3-2 win over Finland.
Lorenzo Canonica and Jeremy Jabola also scored for Switzerland (1-0-0). Jonas Taibel had two assists, while Kevin Pasche stopped 14 shots.
Konsta Kapanen and Kalle Vaisanen replied for Finland (0-0-1). Aku Koskenvuo made 24 saves.
Finland entered the tournament having been the runners-up at the last world juniors, falling to Canada 3-2 in overtime in August. The tournament was rescheduled due to an outbreak of the COVID-19 Omicron variant.
The United States were scheduled to take on Latvia and Canada begins its title defence against Czechia later in the day.
Sweden routs Latvia
Filip Bystedt and Isak Rosen each had two goals and an assist as Sweden got off to a blazing start at the world junior hockey championship on Monday with an 11-0 drubbing of Austria.
Carl Lindbom had 13 saves in earning a shutout, while also dishing out an assist for Sweden (1-0-0).
Thomas Pfarrmaier stopped 23-of-29 shots in 30:28 of action before being pulled for Benedikt Oschgan, who allowed five goals on 22 shots for Austria (0-1-0).