Thomas Chabot and Zach Sanford scored for the Senators (12-20-3) as Matt Murray made 30 saves. Vitek Vanecek stopped 20 shots in the Capitals (23-10-9) goal as Alex Ovechkin (2) and Nicklas Backstrom found the back of the net.
"You don't like the way you end up getting a point because we kind of gave them that one in overtime but certainly we gave ourselves every chance to win," Sens head coach D.J. Smith said.
Knotted at 2-2 heading into the extra frame, Backstrom won the game as he stole the puck from Josh Norris and then outwaited Murray before he lifted the puck high for the game-winner at 1:13.
"We had a good first two periods but with a skilled team like that you can't have any breaks and let off the gas," Alex Formenton said. "In the third they put us a little bit on our heels and then [it was] just a bad bounce in OT."
The Senators had just three shots in the first period but found themselves up 1-0 after 20 minutes thanks to Chabot's second of the year as his point shot evaded traffic at 1:22. It was a defensive showing by both teams in the frame as Washington didn't tally its first shot of the game until there was less than three minutes left when they were awarded a power play late in the period.
"That's how you've got to play on the road," Smith said. "You've got to bore them a little bit … we did everything to script."
Ottawa's lead was 2-0 at 6:07 of the second through Sanford's seventh of the year. Formenton brilliantly setup the goal as he collected the puck on the right side boards, slipped past Nic Dowd, deked-out Dennis Cholowski, and then slid a backhand pass to Sanford who was out front as he doubled the Senators' lead.
"We supported each other great tonight," Sanford said of his linemates Formenton and Tim Stützle.
Ovechkin got the Caps on the board 1:39 into the third as Trevor van Riemsdyk's shot from the right goal line hit the post and bounced out in front where the Russian buried his 28th goal of the season.
He'd have the 759th tally of his career with 10:17 to play as he buried Nicklas Backstrom's centering pass up high to make it a 2-2 game.
"Give them credit but at the same point we left Ovechkin open in the slot twice and he isn't going to miss those," Smith said. "We had to get through the first six minutes of the third and skate a little bit more."
The Sens complete its three-game road trip Sunday when they visit Columbus.
"There's a lot of good things we did tonight and we have to turn the page tomorrow," Formenton said. "After a loss it's nice to turn the page and play the next day.
"It's fresh in your mind the mistakes you made but it's fresh in your mind the good things you were doing."
Puck drop Sunday is at 6 p.m.
