Steven Stamkos scored with 63 seconds left in the game as Tampa Bay played spoiler on Monday with a 4-2 win over Washington.
Washington remains the eighth-seed in the Eastern Conference with two games to play, but holds just a two-point lead over Buffalo, which has three games remaining.
Stamkos added an empty-netter in the final second for his 58th goal of the year and also had an assist for the Lightning, who are already eliminated from the playoffs. Dwayne Roloson had 31 stops in Tampa Bay's second straight victory.
Alexander Semin had a goal and an assist while Jason Chimera also scored for the Capitals, who had won their previous two. Michal Neuvirth gave up three goals on 26 shots in the loss.
Washington had tied the game with 3:17 to play on Chimera's 20th of the year, but Stamkos lit the lamp to give Tampa a lead with 1:03 left.
A slap shot from the left point by Brian Lee hit a body in front and went to the right where Stamkos slammed it home.
Stamkos then scored with the net empty in the final second on a shot from his knees along the right boards.
The first period passed scoreless, but the Capitals took a 1-0 lead 12:47 into the second. A turnover in the Tampa end along the right boards saw Matthew Perrault get the puck. He immediately passed it over to the top of the right circle where Semin one-timed it home for his 20th of the year.
Tampa, though, responded with a pair of goals separated by 25 seconds later in the second period.
The first came on the power play when Stamkos sent a pass from the right circle to the left where Teddy Purcell blasted a slap shot between the pads of Neuvirth at the 17:20 mark.
Moments later, Victor Hedman blasted a slap shot from the left point that found the back of the net with Purcell providing a screen in front for a 2-1 advantage.
The Caps tied the game when Semin grabbed the puck at the right side and passed it to the front where Chimera slapped it home.
Washington has a home game against Florida on Thursday and a road game against the Rangers on Saturday to close out the regular season...Tampa, which went 25-14-2 at home this season, plays three games on the road to close out the campaign starting on Wednesday in Montreal...Each team won three times in the season series...Tampa went 1-for-4 on the power play while Washington was 0- for-2...Stamkos has 95 points on the season.