Tim Stutzle scored with 15.3 seconds remaining in the second period to start Ottawa's comeback from a two-goal deficit. DeBrincat tied the score with 5:43 left in regulation and won it 1:31 into 3-on-3 OT.
''I thought we played well,'' said DeBrincat, a 41-goal scorer last season with Chicago who now has 13 through 35 games with the Senators. ''They're a good team. They've been on a hot streak right now, and we did a good job of shutting them down for the most part.''
Cam Talbot bounced back from allowing two goals on the first eight shots he faced to make 22 saves. Rookie defenseman Jake Sanderson also scored to help the Senators win a second game in a row.
''We battled back,'' Sanderson said. ''Thought there was probably like five minutes throughout the game where we weren't ourselves, but we battled back and we felt like we deserved this one.''
Alex Ovechkin scored his 23rd goal of the season and 803rd of his career for Washington, which lost for the first time since Dec. 15. Dylan Strome and Evgeny Kuznetsov also scored for the Capitals, and Darcy Kuemper made 41 saves in his second consecutive start.
''Obviously, he was stunning tonight and he was stunning (Tuesday) against New York,'' Ovechkin said. ''It's tough loss, it's on us and we can't do that.''
The Capitals were in a giving mood in their second game after the NHL's holiday break, handing the Senators several quality scoring chances on odd-man rushes and breakaways. The stingy defense that was the backbone of their run of 10 victories in 11 games faltered in several instances, and Kuemper, despite some big stops, could not bail out his teammates.
''They were the better team tonight from the start to the end,'' coach Peter Laviolette said. ''Lesson to be learned for us that we can't come out that way.''
After rolling along amid several injury absences, the accumulation caught up to Washington in the second consecutive game without top defenseman John Carlson, who took a puck to the face and is out indefinitely, and fifth in a row without winger T.J. Oshie, who has an upper-body injury.
The Senators have been dealing with plenty of injuries, too, but are slowly creeping up the Eastern Conference standings after some big offseason expectations and a slow start. This victory was thanks in large part to veteran free agent addition Claude Giroux, who dived to keep the puck in on Stutzle's goal and assisted on DeBrincat's overtime winner.
''He's a really, really competitive guy,'' coach D.J. Smith said. ''He did his job, and when he got his chance, he made good on it.''
NOTES: Capitals defenseman Erik Gustafsson extended his point streak to six games. Kuznetsov is on a four-game point streak. ... Washington assistant coach Scott Allen missed the game because of COVID-19 protocol. Center Nicklas Backstrom, who appears to be nearing his season debut after offseason hip surgery, went into protocol Wednesday.
Senators: Visit the Detroit Red Wings on Saturday night.
Capitals: Host the Montreal Canadiens on Saturday afternoon.
Follow AP Hockey Writer Stephen Whyno on Twitter at https://twitter.com/SWhyno
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