Brianne McLaughlin-Bittle made 11 saves, and Shiann Darkangelo had two assists for the Americans, coming off a 3-2 loss to Canada on Wednesday night. Canada faced Finland on Friday night in the round-robin finale. The championship game is Saturday night.
Sara Grahn made 47 saves for Sweden.
"Their goalie played a really great game," Knight said. "She made a lot of really great saves, but it wasn't frustrating for us at all. We're a relentless team."
Knight opened the scoring in the first period. The U.S. outshot Sweden 22-2 in the period.
"We just had to continue our energy and keep our momentum," Knight said. "There's unfortunate bounces that can happen here and there throughout a game. Luckily, we just stayed on our toes and kept at it."
Pfalzer and Decker added second-period goals. Pfalzer scored on a 5-on-3 power play, and Decker had a short-handed goal.
"We had a lot of energy," U.S. coach Ken Klee said. "Great chances, moving the puck, moving our feet — those are the things we have to pride ourselves in. It was a fun game."
The United States finished round-robin play 2-1, also beating Finland on Tuesday night.
Sweden (0-3) will play Finland in the third-place game.