Canada opened up their World Junior title defence in the primetime slot on the opening day of the tournament, taking on main rival USA; one of the teams with a legitimate shot at claiming this year's gold medal.
The lack of discipline shown by Canada in pre-tournament play showed up just moments into the game, with Dylan Strome called for slashing after pestering US defenceman Louis Belpedio as he swung around his net. The US had some good zone time on the early power play, but was unable to capitalize on the early opportunity.
Once back to five-on-five, it was Canada's Brendan Perlini who was the standout player of the first frame, getting several good chances, including a shot with three minutes to go that seemed to be headed in the net, but a desperation attempt by US goaltender Alex Nedeljkovic was enough to get the puck to go off the underside of the top of his blocker and out the other side.
A few seconds later, it was the USA who was punished for a lack of discipline, as Alex DeBrincat — one of the team's most dangerous offensive players — speared Travis Konecny in front of the benches, and received a major penalty and a game misconduct as punishment, sending Canada to a five-minute power play.
Canada had a few shots on a man advantage that spanned the first intermission break, but was never able to create any sustained pressure.
Minutes after the power play, Julien Gauthier blocked a shot near his defensive blue line and launched a rush with Rourke Chartier the other way. Nedeljkovic made a great stop on an initial cross-crease pass to Chartier, but the puck dropped right in front of Gauthier at the side of the net, who made a great pass from his knees to a trailing Mathew Barzal. Barzal fired the puck into the top corner as Nedeljkovic hadn't yet recovered from making the sliding save.
The goal seemed to wake the US up, as they controlled the play afterward and had Canada on their heels and icing the puck repeatedly, forcing head coach Dave Lowry to use his timeout midway through the second period. The intervention proved successful, as the American barrage relented to allowed Canada to find their legs once again.
Late in frame, an offensive-zone faceoff win led to a missed shot by Sonny Milano, but Colin White beat Haydn Fleury to the opposite of the net and pounced on the rebound off the back boards to tie the game up at one goal apiece.
Six minutes into the third period, Nedeljkovic initiated contact with John Quenneville outside of his crease, his dive not bought by the official standing 10 feet away, but getting the call from the referee at centre ice. On the ensuing power play, American captain Zach Werenski's point shot got through traffic in front of the net and by Mason McDonald to put the US on top.
With Werenski in the box for slashing moments later (perhaps as the result of a make-up call for the earlier gaffe), Dylan Strome walked into the middle of the ice and fired a shot past Nedeljkovic to even things up once more.
With just over three minutes remaining, however, Joe Hicketts attempted to knock down Belpedio's point shot, instead tipping it perfectly past McDonald to give the US a late third-period lead.
Auston Matthews extended the lead to 4-2 just seconds later, jumping on a puck that had squeaked through McDonald's five hole to sit just in front of the goal line. Canada pulled the goaltender and had lots of in-tight scoring chances, but were ultimately unable to get anymore behind Nedeljkovic.
The regulation loss will make it very difficult for Canada to claim top spot in Group A, meaning they will likely face a tougher opponent in the quarter-finals.
Canada will look to get their first win of the event on Monday afternoon at 1:00 PM EST, when they take on Team Denmark.