A playoff berth can wait. The Ottawa Senators will take a win in the NHL's toughest arena against the league's best team.

The Senators outperformed Washington's lethal offence by making them pay when down a man, scoring three power-play goals including once in overtime for a 5-4 victory on Tuesday night.

After Capitals' star forward Nicklas Backstrom was whistled for tripping, Erik Karlsson's pass from the point was redirected by Alex Kovalev from the side of the net and past goaltender Jose Theodore with 18 seconds left in the extra period.

Jason Spezza won the draw on the winning goal and had four points for the Senators, who won their fifth straight but failed to clinch a spot in the post-season because playoff contenders Atlanta and the New York Rangers also won Tuesday.

"At this time of year, not only do you want to win games, but you want to feel good about how you're playing, too," Spezza said. "Confidence is huge this time of year, and there's a big difference between the win and the loss and how the mood is in the room the next day."

The loss was the third straight for Washington (49-15-12) and just their 10th on home ice in 37 starts this season.

Ottawa's newly formed top forward line of Peter Regin between Daniel Alfredsson and Spezza combined for eight points. Regin extended his points streak to five games with his 13th goal of the season, while Alfredsson collected three assists and has three goals and 13 points during an eight-game points streak.

Karlsson also set up three goals for the 42-30-5 Senators, who opened up a seven-point lead on sixth-place Philadelphia in the Eastern Conference.

Valiant comeback

It was a valiant comeback by the Senators, who frittered away a 3-1 lead in the second period and overcame a 4-3 deficit in the third against a Capitals outfit that tops the NHL with 296 goals this season.

With the Senators down 4-3, Spezza picked up his fourth point of the night as Mathieu Perreault, who scored 24 seconds into the third period, sat in the penalty box for interference.

Spezza took a pass from Mike Fisher low in the Washington zone and let go a shot from a bad angle that appeared to hit Capitals defenceman Jeff Schultz and elude Theodore, who saw his record slip to 17-0-3 in his last 20 appearances.

The five goals against just two days after Theodore was pulled in the first period of a 5-3 loss to Calgary has Washington head coach Bruce Boudreau concerned.

"I don't like five goals against," Boudreau said. "That has happened twice in a row and we've got to get better. There were four pretty iffy goals out there tonight."

The Senators power play ranked 26th in the 30-team league to begin Tuesday's contest but converted six of 13 chances in the four-game season series.

Chris Campoli, Regin and Spezza, with his first of two power-play goals on the night, gave Ottawa a 3-1 advantage in the first period.

1st period woes

But Washington, which has been outscored 9-1 in the first period the past three games, beat Brian Elliott — the NHL's reigning No.1 star of the week — twice on 10 shots in the second.

Alex Ovechkin set up Alexander Semin for his second goal of the contest and 37th of the season by going wide on defenceman Brian Lee — subbing for the injured Anton Volchenkov — and feeding the puck to his open teammate, who lifted a shot over a fallen Elliott.

Defenceman Mike Green drew the Capitals even just 54 seconds later on a one-timer from inside the faceoff circle for his 18th goal of the season.

"Maybe we're not ready for the first period," Backstrom said. "We have to, because I remember last year in the playoffs we weren't ready the first two games. So we have to get ready now and play a good 60 minutes. We haven't played a good 60 minutes in a while."

Elliott made 17 saves while allowing as many goals as he has done in his last four games, when he went 4-0 with a pair of shutouts.

"I didn't have one of my best nights," Elliott said. "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 put out a win."

The Senators host Carolina Thursday at 7:30 p.m. ET ahead of a three-game road trip.