Ridly Greig (17:42) and Shane Pinto (18:42) added empty-net goals for the 4-1 final.
“I don’t think anybody wants the playoffs more than the guys in this room,” Ottawa captain Brady Tkachuk said.
Dylan Cozens also scored for the Senators (39-26-10), who had lost three in a row (0-2-1). Linus Ullmark made 21 saves.
“It was a great job by our group,” Cozens said. “(Buffalo’s) a really good team, they’ve been playing great hockey. So for us to just dig in and grind one out there, I’m proud of this group.”
The Senators moved into the second wild card from the Eastern Conference with the win. They are tied in points with the Detroit Red Wings and Columbus Blue Jackets but own the tiebreaker over both. Columbus held the spot entering the night but lost 5-1 at the Carolina Hurricanes.
“The one thing about our team, I’ve said it before, they’re very coachable and you can be very honest with them about their game, and they responded tonight," Ottawa coach Travis Green said.
Mattias Samuelsson scored the lone goal for the Sabres (46-22-8), who had won two straight and were looking to clinch a playoff berth for the first time since 2010-11. Luukkonen made 20 saves.
Buffalo is tied in points for first place in the Atlantic Division with the Tampa Bay Lightning, who defeated the Pittsburgh Penguins 6-3 on Thursday and have played one fewer game. The Sabres are only two points ahead of the Montreal Canadiens, who also have a game in hand and won 3-2 at the New York Rangers.
“I mean, energy was super high,” Samuelsson said. “Obviously, we know the stakes with a win. Yeah, disappointing for sure, but obviously not the end of the road for us where we're standing. Just have to get back to work and put on a better performance in two days.”
After a scoreless first period during which Buffalo outshot Ottawa 6-4, the Sabres struck first in the second.
Samuelsson took a pass from Bowen Byram at the left point, skated to the top of the circle, and scored through a screen to give Buffalo a 1-0 lead at 8:49.
“If we want to be able to do anything in the postseason, we're going to have to find ways to win different ways,” Samuelsson said. “And we definitely didn’t do that tonight.”
Cozens tied the game 1-1 at 15:18 of the second. Greig knocked down Rasmus Dahlin's clearing attempt at the left point and passed over to Tkachuk, who then sent a feed down low to Cozens, who had gotten behind Dahlin and redirected the puck with one hand on his stick past Luukkonen.
“It was a weird game to start, not a lot going on,” Cozens said. “But we stuck to the process of just playing how we want to play and just grinding it out, and we just found a way to win.”