Noah Hanifin (Carolina Hurricanes) and Dylan Larkin (Detroit Red Wings) each had a goal and an assist for the U.S., and Miles Wood (New Jersey Devils) and Chris Wideman (Ottawa Senators) also scored. Goaltender Mike Condon (Montreal Canadiens) had 20 saves.
Matthews' first goal, on the power play at 14:25 of the second period, gave the U.S. a 5-1 lead. He settled a bouncing puck and scored under the crossbar with a shot from the bottom of the left circle.
After Belarus cut the U.S. lead to 5-3, Matthews scored the game's final goal at 14:40 of the third period. He took a pass from Frank Vatrano (Boston Bruins) at the hash marks and scored over the glove of goaltender Kevin Lalande.
Wood gave the U.S. a 1-0 lead in the first period, and then Matthews set up Wideman's power-play goal at 13:38 of the first.
Goals by Larkin and Hanifin in the second period sandwiched a goal by Belarus' Geoff Platt to give the U.S. a 4-1 lead.
The U.S. is tied with Canada, Finland and Slovakia for first place in Group B with three points but is the only one of the four to play two games. The U.S. lost to Canada 5-1 in its tournament opener Friday. It next plays Monday against Finland.
OTHER RESULTS:
Kazakhstan 3, Switzerland 2 (SO):Nigel Dawes scored twice in the shootout and Kazakhstan beat Switzerland in a Group A preliminary-round game at Ice Palace in Moscow.
International rules allow teams to use the same shooter an unlimited amount of times after the third round of the shootout.
Dawes, who played in the NHL with the New York Rangers, Atlanta Thrashers, Arizona Coyotes and Montreal Canadiens, had missed on a first-period penalty shot.
Vitali Kolesnik made 49 saves through overtime and had four saves in the shootout.
Raphael Diaz (New York Rangers) and Sven Andrighetto (Montreal Canadiens) had assists for Switzerland on Samuel Walser's first-period goal, and Reto Berra (Colorado Avalanche) stopped 24 shots.
