The loss snaps the U.S.' 12-game win streak against Sweden in the tournament, dating back to 1996.
Alexander Nylander scored in the second period and Linus Soderstrom pitched a 46-save performance for Sweden to hand Team USA a 1-0 loss in Group A in the 2016 World Junior Championship on Monday at Helsinki Ice Hall.
Nylander took a feed from fellow Maple Leafs prospect Dmytro Timashov for a breakaway then went top shelf on Hurricanes prospect Alex Nedelijkovic for the game's lone goal.
The Americans were given plenty of chances to tie the game.