Cowen, a rookie defenseman, scored on a redirection from the slot 45 seconds into the extra period, giving Ottawa a 3-2 victory over the Buffalo Sabres on Tuesday night.
With forwards Jason Spezza and Peter Regin back, the defensemen went to the net. Cowen pinched into the slot and took a pass from fellow blueliner Erik Karlsson in the right corner. Karlsson was fed from the point by Spezza, his second assist of the night.
"I just went to the net and Karlsson saw me, a great pass and I just touched it in there," Cowen said of his third career goal and first game-winner. "When I was going down, I was thinking it was a gamble, wasn't sure if I should be there. Obviously it worked out."
It's not the type of play Spezza prefers to see become a habit.
"You try to get your 'D' involved in the rush, but not both of them," Spezza said. "I don't know if we want both guys jumping in, but we'll take it."
The Sabres were taken by surprise, too.
"It kind of threw (our) forwards off," Buffalo forward Derek Roy said. "You have to find your guy and make coverage."
Milan Michalek and Regin also scored for Ottawa, which trailed 2-1 in the first period.
Michalek, who leads the NHL with 19 goals, left with 5½ minutes remaining in the second after colliding with Karlsson. Senators coach Paul MacLean said Michalek would be re-evaluated when the team returned to Ottawa, where the club plays Boston on Wednesday.
"He's a big cog to our team," Spezza said. "He's a guy that works hard and makes a difference."
Craig Anderson stopped 27 shots.
"We've been nowhere near good enough at home all year," Miller said. "I don't think it's time to panic, but it's time to build the game that we need to be competitive and be a playoff-caliber team."
Buffalo will wrap up its five-game homestand Friday against Toronto.
"I'm tired of could-haves," coach Lindy Ruff lamented. "It's how poorly we defended the first goal and how we defended that overtime goal."
Regin tied the game 7½ minutes into the third period, when his point shot got through a screen in front of Miller.
Buffalo got off to yet another slow start as Michalek scored just 69 seconds into the game. As Miller appeared to lose sight of the puck, bouncing in several different directions, Spezza delivered a drop pass to Michalek in the slot for an easy one-timer.
The Sabres came back with 5:44 left in the first when Szczechura scored on a backhander after breaking up a pass in the slot. Just 88 seconds later, Ennis put the Sabres up on a wrist shot from the slot, following a nice feed by Drew Stafford in the left circle.
It was Szczechura's first NHL goal since March 25, 2010, with Tampa Bay at Boston.
Buffalo had its six-game winning streak against Ottawa snapped. The Sabres are 8-1-1 in the last 10 games of the Northeast Division rivalry.
"It feels like it's a little bit between the ears and the guys need to get that trust," Miller said. "By the time you think through a situation, it's gone. Hockey moves too quick. You have to be in the flow and right in the mix of the game."
The Senators hope Michalek won't be sidelined too long after he attempted to break a fall with his right arm and instead landed on his shoulder.
"I read the guy's pass and stepped up and I think Milo was coming full speed to back-check," Karlsson said. "I was only looking for their guys and not ours, and we collided pretty hard there. We were both going forward. It's just bad luck. I didn't see him coming."
Michalek has scored a goal in six of his last eight games. ... D Mike Weber, who missed 11 games with a broken rib, returned to the Buffalo lineup, along with C Paul Gaustad, who sat out three games with an upper-body injury. ... Szczechura, who was injured throughout training camp and had been a game-day call-up for his first three games, appeared in his fifth game and centered for Thomas Vanek and Jason Pominville. ... Ottawa C Nick Foligno played in his 300th NHL game. He has points in six of his last eight. ... The Senators have been outscored 33-20 in the first period.