Trailing 4-1, the Panthers scored four goals on a season-high 27 shots in the third period to snap a two-game skid.
''It was pretty quiet in between periods,'' Reinhart said. ''We kind of knew what needed to be done and it was great to be able to turn that game around. The depth showed. We're happy with the effort.''
Florida's rally was beyond improbable. NHL teams had lost 303 consecutive games when trailing by three or more goals entering the third. The last team to pull off such a comeback was, ironically, the Capitals - who on Jan. 18, 2020, trailed the New York Islanders 4-1 entering the third and went on to win 6-4.
The Capitals were called for goalie interference with just under a minute to play, and the Panthers made the most of it when Reinhart's shot from the left circle squeezed between goalie Ilya Samsonov and the post.
Eetu Luostarinen and Ryan Lomberg each had a goal and an assist for the Panthers, while Sam Bennett and Joe Thornton also scored. Aaron Ekblad had three assists, and Jonathan Huberdeau had an assist on each of the last two goals. Sergei Bobrovsky stopped 23 shots and is 8-0-0 at home.
Nick Jensen had a goal and an assist for the Capitals. Lars Eller, Beck Malenstyn and Connor McMichael also scored goals. Dmitry Orlov had two assists, and Samsonov made 45 saves.
The Capitals lost for the first time in four games.
''We stopped playing,'' Capitals coach Peter Laviolette said. ''That is two games in a row that we've stopped playing in the third period. If you don't punch back, the only thing you are going to do is get punched and we got punched for 20 minutes. It's on us.''
Lomberg's goal at 3:23 of the third made the score 4-2. Luostarinen scored a shorthanded goal with about six minutes left in the third to close the Panthers to 4-3. Then Bennett tipped in a shot from Aaron Ekblad that tied the score at 4 with 7:59 left before Reinhart capped the scoring.
''There's always a belief in that room that we're never out of it,'' Lomberg said. ''As soon as the first domino fell, we just kept our foot on the gas.''
The Capitals took a 2-0 lead when they scored two goals by McMichael and Malenstyn 11 seconds part in the first. But Thornton's goal, an easy tap-in of a rebound, closed the score to 2-1 at 6:55 of the first. Thornton now has 1,533 career points, tying Mark Recchi for the 12th most in NHL history.
''I think we let our guard down a little bit and we kind of thought that game was already over,'' McMichael said. ''It is just unacceptable and we have to be a lot better than that.''
Eller's backhander that got past Bobrovsky stretched the Capitals' lead to 3-1 at 6:40 of the second, and Jensen made the score 4-1 on his shot from the high slot with 7:20 left in the second.
Barring a playoff matchup, Tuesday was the third and final meeting this season between the Panthers and Capitals - a very early end to the series. Florida hasn't even started its season series with 17 other teams, and Washington has yet to play 12 clubs.
NOTES: Ovechkin entered the game with 378 regular-season goals on the road in his career. Only Wayne Gretzky has more (402). ... This is only the third season in which the Panthers have had more than 13 wins at the end of November. The others were 1995-96 (17, in 24 games) and 1996-97 (16, in 24 games). This was Florida's 22nd game of this season.
Capitals: Host Chicago on Thursday.
Panthers: Host Buffalo on Thursday.
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