Washington have frustrated Philadelphia by killing their power plays on the way to a 2-0 opening NHL Eastern Conference first-round play-off win.
In Thursday's other Eastern Conference opener, New York edged Florida in a nine-goal encounter, while in the West, San Jose narrowly beat Los Angeles and Dallas comfortably overcame Minnesota.
Washington's penalty kill went for 4 for 4 while goaltender Braden Holtby produced seven saves during the Flyers' power plays and 19 in all.
The Capitals did take their chance on the power play, with John Carlson scoring in the second period with a shot that deflected in off teammate Chris VandeVelde. Jay Beagle added a late goal.
Philadelphia lost second-line centre Sean Couturier to an upper-body injury in the second period.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Game 2 is on Saturday in Washington.
New York downed Florida 5-4, with John Tavares contributing a goal and two assists, including one that set up Kyle Okposo's go-ahead goal early in the third period.
Thomas Greiss survived a shaky beginning and made 42 saves for the Islanders in his first play-off start and Brock Nelson, Frans Nielsen and Ryan Strome added goals for New York.
Home-ice advantage now belongs to the Islanders and they can take a 2-0 lead back to Barclays Center if they prevail when the series resumes in a quick turnaround on Friday.
Reilly Smith had two goals, Jussi Jokinen had a goal and two assists and Teddy Purcell also scored for the Panthers. Roberto Luongo made 21 saves.
San Jose's Joe Pavelski broke a tie with his second goal of the game early in the third period and the Sharks hung on to take an important 4-3 win in Los Angeles.
Brent Burns and Tomas Hertl scored for the Sharks in their first post-season game since losing four straight to the Kings in 2014, completing a seven-game flop in the first round.
LA rode the momentum then to their second Stanley Cup title but both California rivals missed the play-offs last year.
San Jose's Martin Jones made 19 saves against his former Los Angeles teammates in his first career play-off start.
Game 2 is on Saturday at Staples Center.
Dallas' Jamie Benn had a goal and two assists in the Stars' 4-0 win against Minnesota.
Kari Lehtonen made 22 saves for his second career play-off shutout while Jason Spezza returned to the post-season with a nifty goal and added an assist.
Spezza was skating along the right side and initially faked a slap shot with just over 8 minutes left in the second period.
Game 2 is on Saturday in Dallas.
