Declan Chisholm passed across the slot to van Riemsdyk, who was going to the net and poked the puck over Dan Vladar to end a 38-game goal drought.
Aliaksei Protas had a goal and an assist, and Rasmus Sandin scored his first goal in 40 games for the Capitals (30-23-7), who have won five of six. Logan Thompson made 23 saves.
Noah Cates scored for the Flyers (25-21-11) who have lost six of seven. Vladar made 26 saves.
It was the first game for each team following the break for the Olympics.
Sandin gave the Capitals a 1-0 lead at 13:52 of the second period. Jakob Chychrun passed to Hendrix Lapierre below the right circle. Lapierre passed across the slot to Sandin cutting through the left circle and he beat Vladar with a wrist shot from just inside the circle.
Cates tied the score 1-1 at 29 seconds of the third period when he tipped Travis Sanheim’s point shot past Thompson from in front after Protas turned the puck over in the defensive zone.
Thompson made a left pad save to rob Matvei Michkov’s at the right post at 9:55.
Protas scored a short-handed goal into an empty net during 6-on-4 play at 19:34 for the 3-1 final.
