Washington had its four-game winning streak snapped and missed a chance to clinch its fourth straight Metropolitan Division title. The defending Stanley Cup champions lead the New York Islanders, who lost to Toronto, by three points with two games to play.
"Obviously it would have been nice to clinch it, but we've got two more chances," Nicklas Backstrom said. "Hopefully we can get it done."
The Capitals play their final two regular-season games at home, against the Canadiens and Islanders.
Barkov has 94 points this season, tying Pavel Bure for the franchise record set in 1999-00.
"My biggest goal is to make the playoffs and win the Stanley Cup, but of course it's a nice milestone for me," Barkov said.
Roberto Luongo made 27 saves as the Panthers won their third straight game with him in net.
"I thought (Luongo) was amazing," coach Bob Boughner said. "He made some big saves. Even at the end when Washington turned it up a notch and it's a 6-on-5, he held strong. He was a big part of our win tonight."
After trailing 4-0, the Capitals scored three times in the third period.
Kuznetsov redirected a shot from the point by John Carlson past Luongo to make it 4-1 with 9:05 left. Backstrom's one-timer pulled the Capitals to 4-2 with 3:35 remaining. Vrana's shot from the right side made it 4-3 with 2:21 to go.
"We weren't sharp to start the game and they were able to convert on their chances," Capitals coach Todd Reirden said. "They got some good opportunities and they finished. We didn't get ours until the game was out of reach."
Trocheck's second goal, an empty-netter with 26.5 seconds left, pushed the lead to 5-3.
Huberdeau stretched the Panthers' advantage to 2-0 with a shot from the low slot that beat Copley at 3:34 of the second. Trocheck's short-handed goal at 12:01 made it 3-0. Trocheck skated in on Copley and beat him between the legs.
Brouwer made it 4-0 when he put the puck behind Copley with 2:03 left in the second.
Vatrano gave the Panthers a 1-0 lead when his shot from the slot went over Copley's glove and high into the net with 6:12 left in the first.
"We came out with nothing to lose and played hard," Trocheck said.
Capitals forward Brett Connolly played after sitting out a 6-3 win Saturday against Tampa Bay due to illness. ... Trocheck's goal in the second was the Panthers' second short-handed goal in two games and third this season. ... The Panthers went 3-0-0 against the Capitals and swept the season series for the first time.
Capitals: Host the Montreal Canadiens on Thursday.
Panthers: Host the New York Islanders on Thursday.
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