The win gave the Senators 89 points, fifth in the Eastern Conference. They could have clinched a playoff berth, but Atlanta and the New York Rangers both won their games. Ottawa can assure itself of a trip to the playoffs by beating Carolina at home on Thursday.
Capitals coach Bruce Boudreau did not think Backstrom had been on the ice for too long, but the Swedish center's shift had reached 1:02 when he tripped Kovalev along the boards in the Ottawa zone.
It was only Ottawa's fourth power play of the game, and the Senators were able to convert before a potential shootout.
"If it is blatant they are going to call it -- it was probably a dumb penalty if you ask me," Capitals center David Steckel said. "Thirty seconds left in the OT -- he's not going to beat you up the ice. They're going to call it and it resulted in a goal tonight."
Mathieu Perreault gave the Capitals their first lead of the evening with his second goal in as many games 24 seconds into the final period. Perreault took a pass from Eric Fehr and chipped a shot into the top right corner from in tight to make it 4-3.
Perreault also helped the Senators get even by taking an interference penalty behind the Ottawa net later in the period. Jason Spezza scored his second of the night when he put a shot from the goal line off the inside of Jose Theodore's leg and into the net at 5:14 with the Senators on the power play.
Theodore yielded five goals on 31 shots, and the Capitals have allowed 10 goals in the past two games.
"I don't like five goals against," Boudreau said. "This has happened twice in a row and we gotta get better. There were four pretty iffy goals out there tonight."
Peter Regin put the Senators on the board first with a backhander from the right circle at 1:24 of the opening period. Ottawa capitalized on a pair of gaffes by Washington's new-look top line of Backstrom, Alex Ovechkin and Alexander Semin on the play -- one errant pass near the team's blue line and then a turnover behind the net by Backstrom.
Regin's shot was Ottawa's first of the contest, and Semin returned the favor 1:37 later. He collected a long pass from Theodore with the Capitals on the power play and weaved to the middle of the ice before turning and firing a shot through Brian Elliott's legs.
The Senators countered with a power-play goal of their own 90 seconds later. Spezza deflected a shot from the top of the offensive zone by Matt Cullen that beat Theodore after defenseman Shaone Morrison knocked Mike Fisher into his goaltender.
Chris Campoli extended Ottawa's lead late in the opening period. Senators captain Daniel Alfredsson found Campoli trailing the play, and he skated in unimpeded on Theodore and was able to poke his own rebound into the net at 16:06.
Slow starts have plagued Washington of late. The Capitals have allowed nine first-period goals in their last three games.
"We didn't come out ready to play and it hurt us in the end," defenseman Tom Poti said. "We weren't picking up loose guys in front. None of those goals were [Theodore's] fault."
Washington was able to bounce back and tie the score with a pair of second-period goals. Semin registered his second of the night at 12:04 of the middle period. It appeared Ovechkin might have a breakaway after a long breakout pass from Backstrom, but Karlsson recovered to nullify it. Still, Ovechkin was able to slip a pass to Semin alone in front of the net and roofed a backhander for his 37th of the season -- one shy of his career high.
Mike Green made it 3-3 just 54 seconds later. Jason Chimera won a battle and got the puck to Poti, who sent a D-to-D pass to Green for a shot that hit Elliott and trickled into the net.
"They don't make it easy on you," Elliott said. "I didn't have one of my best nights, but it shows that we are becoming a pretty good team when your goalie doesn't have his 'A' game - or close to it - but we can still pull out a win."
The Caps were still without forward Brooks Laich, who skated Tuesday morning. Boudreau said he has been cleared to play. Laich has missed four games after taking a puck off his face in practice last week. Defenseman John Carlson did not play in the final 27 minutes, and Boudreau said he had an "upper body bang" but could be ready to play Thursday against Atlanta.
|Peter Regin (13) ASST: Jason Spezza (28), Daniel Alfredsson (45)|
1 - 0 OTT
|PPG - Alexander Semin (36) ASST: Jose Theodore (2)|
1 - 1 Tie
|PPG - Jason Spezza (21) ASST: Matt Cullen (31), Daniel Alfredsson (46)|
2 - 1 OTT
|Chris Campoli (4) ASST: Daniel Alfredsson (47), Jason Spezza (29)|
3 - 1 OTT
|Alexander Semin (37) ASST: Alex Ovechkin (55), Nicklas Backstrom (62)|
3 - 2 OTT
|Mike Green (18) ASST: Tom Poti (19), Jason Chimera (18)|
3 - 3 Tie
|Mathieu Perreault (4) ASST: Eric Fehr (17)|
4 - 3 WSH
|PPG - Jason Spezza (22) ASST: Mike Fisher (28), Erik Karlsson (19)|
4 - 4 Tie
|PPG - Alex Kovalev (18) ASST: Erik Karlsson (20), Daniel Alfredsson (48)|
5 - 4 OTT
|Erik Karlsson Tripping against Alex Ovechkin|
|Matt Bradley Tripping against Daniel Alfredsson|
|Erik Karlsson Boarding against Mathieu Perreault|
|Nick Foligno Hooking against Mathieu Perreault|
|Alexander Semin Tripping against Erik Karlsson|
|Chris Neil Slashing against Alexander Semin|
|Mike Fisher Holding against Nicklas Backstrom|
|Mathieu Perreault Interference against Chris Phillips|
|Nicklas Backstrom Tripping against Alex Kovalev|