Kovalev picked up his 18th goal of the season after Nicklas Backstrom was whistled for a tripping penalty with 33 seconds left in the extra period, handing the NHL standings leaders their third straight loss.
Jason Spezza had two goals and two assists, and Peter Regin and Chris Campoli also scored for the Senators. Daniel Alfredsson added two assists, and Brian Elliott made 17 saves.
Alexander Semin scored his 36th and 37th goals, and Mike Green and Mathieu Perreault also scored for the Capitals. Alex Ovechkin had an assist for his 101st point of the season.
: In Vancouver, British Columbia, Henrik Sedin scored a short-handed goal and added two assists for Vancouver to regain the NHL scoring lead.
Alex Burrows, Mason Raymond and Daniel Sedin also scored, and Roberto Luongo finished with 32 saves as the Canucks moved seven points ahead of Colorado atop the Northwest Division.
Radim Vrbata scored for Phoenix, which remains four points behind San Jose for both the Pacific Division and Western Conference leads.
: In Newark, N.J., Patrice Bergeron scored on a rebound with 18.3 seconds left in overtime and Boston maintained its hold on the final playoff berth in the Eastern Conference.
Tuukka Rask stopped 21 shots to pick up his fifth shutout of the season, keeping Boston two points ahead of Atlanta in the race for the eighth and final playoff spot in the conference.
Bruins defenseman Mark Stuart took a shot from the point that Devils goalie Martin Brodeur stopped, but Bergeron had an open net to deposit his 18th goal of the season.
: In Detroit, Brad Stuart scored with 1:07 left to lift Detroit to the win after the Red Wings blew a 4-0 second-period lead.
Johan Franzen had a goal and an assist, and Andreas Lilja, Nicklas Kronwall and Drew Miller also scored for Detroit, which won its sixth straight. Jimmy Howard stopped 22 shots.
Tom Gilbert scored twice, Mike Comrie added a goal and an assist, and Zack Stortini also scored for Edmonton. Jeff Desluriers made 39 saves.
: In Uniondale, N.Y., Vinny Prospal, Olli Jokinen and Marian Gaborik scored second-period goals, and Marc Staal got the winner early in the third to lift the Rangers.
Henrik Lundqvist posted 25 saves for the Rangers in their third win in four games. New York remains four points behind Boston for the final playoff spot in the East with six games left.
Blake Comeau scored twice and Mark Streit added a goal before the Islanders lost for the fourth time in six contests. The Islanders are 10 points back of the Bruins with six to play.
: In Columbus, Ohio, Rick Nash scored twice for Columbus, including the winner on the second of four consecutive power plays in the first 12 minutes of the final period.
Mike Lundin and Vincent Lecavalier gave Tampa Bay a 2-1 lead heading into the third period. Tampa Bay goalie Antero Niittymaki had 13 of his 22 saves in the final period.
Fedor Tyutin tied it at 6:21 of the third from the high slot with a drive that hit underneath the crossbar before crossing the goal line. Nash scored just over a minute later.
: In Toronto, Nik Antropov scored the winner against his former team to help Atlanta keep its playoff hopes alive.
Maxim Afinogenov and Evgeny Artyukhin scored for Atlanta, which is two points out of the final playoff spot in the East with 80 points. Boston, Montreal and Philadelphia all have 82.
Maxim Afinogenov and Evgeny Artyukhin also scored for Atlanta.
Viktor Stalberg had both goals for the Maple Leafs.
: In St. Louis, Alex Steen had two goals and an assist and scored the go-ahead goal early in the third period, helping St. Louis keep alive faint playoff hopes.
Eric Brewer and Erik Johnson also scored for the Blues, who are six points out of the final Western Conference playoff spot with six games to go.
Patrick Sharp and Marian Hossa scored for Chicago, which lost its seventh in nine games. The Blackhawks have lost three straight in regulation for the first time this season.
: In Nashville, Tenn., one day after being recalled from Manchester of the American Hockey League, Jonathan Bernier made 34 saves to record his first career shutout for Los Angeles.
Scott Parse and Sean O’Donnell scored for the Kings, who ended a four-game losing streak and beat Nashville for the first time since October 23, 2007—a span of seven games. The Predators have lost two of their last three with both losses coming in shutouts.
