Sergei Gonchar's power-play goal 47 seconds into overtime sent the Senators to the postseason as Ottawa eked out a 2-1 win over the Washington Capitals at Verizon Center.
The victory clinched the Senators' second straight playoff appearance as they sit in a three-way tie with the Rangers and Islanders for the last three spots in the Eastern Conference standings, though they have two games remaining while the New York teams only have one.
Ottawa welcomed back Erik Karlsson Thursday, and the reigning Norris Trophy winner assisted on both goals, including Jakob Silfverberg's tally in the second period.
Craig Anderson stopped 19 shots in the win, allowing only one goal on Alex Ovechkin's terrific backhand in the third period.
Michal Neuvirth's 39 saves went for naught, though the Southeast Division- champion Capitals are already locked in as East's No. 3 seed.
"We knew they would be a desperate team and try and create the playoff atmosphere," Capitals head coach Adam Oates said.
Washington's Mike Ribeiro was sent off for roughing with 58 seconds left in regulation. Ottawa's man-advantage bled into overtime, and the extra space allowed Gonchar to fire freely from the top of the right circle. Mika Zibanejad set up a screen in front of Neuvirth, who couldn't stop Gonchar's slapper.
Karlsson saw 27 minutes of ice time a little over two months after suffering a severe cut to his left Achilles. The injury occurred Feb. 13 and was supposed to sideline the star defenseman for 4-to-6 months.
But Karlsson worked his way back and made his presence felt Thursday. Early in the second period of a scoreless tie, he let a rising one-timer fly from the right point that appeared to be heading wide. Silfverberg got a piece of the puck with a pinpoint tip-in that beat Neuvirth with 7:25 remaining in the period.
"I battled some issues out there and didn't feel quite as comfortable as I'm used too, but overall it was a solid game," admitted Karlsson. "I still have to work through some mistakes and clean those up."
Ovechkin, appearing in his 600th career game, tied it in the third when he avoided Anderson's poke check and put in a nifty backhand with 11:29 remaining in regulation.
Ovechkin leads the NHL with 32 goals ... The Sens will host Philadelphia on Saturday before closing the regular season Sunday in Boston ... Washington fell to 10-2-0 in April ... Ottawa swept the three-game season series.