Brooks Laich had two goals and the Capitals secured the second seed in the Eastern Conference playoffs with a 4-2 victory over Tampa Bay on Thursday.
"We're definitely proud of our accomplishments, but we haven't done nothing yet," said Washington defenseman Mike Green, who had a goal and two assists.
Laich and David Steckel scored 31 seconds apart early in the second to gave the Capitals a 3-1 lead.
Washington set a franchise record with 108 points and tied a team mark with 50 wins, matching the 1985-86 team.
"I think you've got to rank this team up there with a lot of them," Capitals coach Bruce Boudreau said. "I think it's quite an accomplishment in today's day and age with the salary cap and all the teams have the ability to be equal. But I think the best team in Capitals history has got to win the Stanley Cup because they've been there and lost it."
The Capitals have won 11 consecutive games against Tampa Bay. It ties an 11-game winning streak from March 12, 1998, to March 15, 2000, against the New York Islanders for the longest victory run over one opponent in team history.
Steven Stamkos and Matt Pettinger scored for the Lightning, who have lost eight in a row and 11 of 12. Tampa Bay will end the season with the NHL's worst home record at 12-18-11.
"We showed some character, came back and made a game of out it," Stamkos said. "It's been a long season. Hopefully we can learn from this season. Learn how it feels to lose and hopefully not have that feeling ever again."
Stamkos set a Tampa Bay record for rookies with his 22nd goal to make it 1-0 just 36 seconds into the game. He had shared the mark with Brad Richards, who had 21 goals during his rookie season in 2000-01.
Laich tied it 1 on a power-play rebound goal at 9:19 of the first.
"It's always nice to score a couple," he said.
Pettinger cut the Tampa Bay deficit to 3-2 with 7:07 left in the third. Green scored an empty-net goal with 4.8 seconds to play.
Washington left wing Alexander Ovechkin, second in the NHL scoring race with 108 points, didn't have a point. The league-leader with 55 goals has not scored in his last three games.
Referee Don Koharski worked his final game, ending a 32-year on-ice NHL career. Many of the players shook hands with Koharski after the game ended. ... Green has 73 points for the season. ... Capitals D Tom Poti (groin) was out of the lineup. With the playoffs upcoming, Washington is taking a conservative approach with Poti, who has missed two straight games. ... Washington G Jose Theodore played in his 500th NHL game. ... Capitals LW Donald Brashear (knee) and C Boyd Gordon (finger) didn't play.