Jakub Voracek and Wayne Simmonds added goals, and Steve Mason made 32 saves to help Philadelphia improve to 12-2-1 in its last 15 games to maintain its hold on second place in the Metropolitan Division.
Jaden Schwartz opened the scoring 6:23 into the game, finishing a 2-on-1 short-handed opportunity after taking a feed from Kevin Shattenkirk. Schwartz's wrist shot from close range went under the glove of Mason.
St. Louis needed one point in the game to become the first Western Conference team to clinch a playoff spot.
It's not always going to be pretty, especially against a great goalie [Lundqvist] like that. My goals are never how you draw them up. It's just a matter of grinding it out and trying to create havoc in front and good things happen.
— Capitals forward Jay Beagle on scoring in their Game 3 victory against the Rangers on Monday