Buffalo scored two goals in the first three minutes of the third period to break a 1-1 tie before a crowd of 16,191 and went on to a 4-2 victory.
"It's a shame," Capitals coach Terry Murray said. "We came out flat in a game in which we had the opportunity to clinch a playoff spot. We had opportunity after opportunity, not only early, but also after it was 3-1, but we couldn't put the puck in the net. Add on the fact that we gave up the puck in key situations that led directly to goals and it's very difficult to win.
"Now we have to go back to the drawing board and find out what happened to us tonight. We have to go into Philadelphia and play a big hockey game on Thursday."
The Capitals still need a win to clinch a playoff berth in the Patrick Division, and it could come tomorrow night at The Spectrum against the Philadelphia Flyers.
The Flyers lost last night to the Pittsburgh Penguins, 3-1, and the New Jersey Devils tied the New York Rangers, 3-3. The tie moved the Devils into a third-place tie for the Capitals, two points in front of the Flyers.
The Buffalo defense was tough enough to hold the Capitals without a shot for more than 20 minutes -- from 8 minutes, 3 seconds of the second period to 10:58 of the third period. During that span, Buffalo opened a two-goal lead.
Dave Andreychuk, who had two goals and an assist, took a shot from the right circle that Tony Tanti deflected past Mike Liut 59 seconds into the third period to put the Sabres ahead, 2-1. Just 1:42 later, former Capital Grant Ledyard scored on slap shot from center point during a power play.
"This was a good win for us," Andreychuk said. "It gives us momentum going into the playoffs. We just about clinched third place [in the Adams Division] with this win. We made Washington turn the puck over a couple of times, and we converted them into goals."
Tanti said: "It was a good team effort, the best we have played i a while. We forechecked very well, and that kept Washington from getting a lot of offensive chances."
The Capitals found their offense again, but it was too little, too late. Dimitri Khristich, scoring his second goal of the game, skated out of the corner, beat Buffalo defenseman Dean Kennedy and put the puck through goalie Daren Puppa's pads to cut the lead to 3-2 with six minutes remaining.
However, Andreychuk, with Mikhail Tatarinov checking him, circled the net and scored on a wraparound goal that went off the post and into the net past Liut with 4:27 remaining. The loss ended a five-game winning streak for the goaltender.
"It was a very tough loss for us," said Capitals right wing John Druce. "Buffalo is a very tough defensive team, and they are very stingy allowing shots. We knew we had to work the puck down deep and not turn the puck over at the blue line. We just never got the chances we needed because of Buffalo's defense.
"We're fighting for our lives now, and we know the game in Philly will be a very big one. We're going into their building, and they are a very physical team. This could the most important game of the season for us."
Rick Dudley, the Sabres coach, said: "We moved the puc quickly, and Washington couldn't come at us and forecheck us as desperate teams like to do. We did the same thing against Philadelphia when we beat them [6-2, Sunday]."
Tim Bergland, trying to explain the Capitals' lack of offense, said: weren't getting the puck down low, and we were playing too much in the neutral zone. We tried to do too much with the puck instead of just putting shots on goal."
Alan May agreed, saying: "We didn't have any zip tonight. Ther was no forechecking. This definitely wasn't playoff hockey. We showed that we have to be ready to play every night. Maybe we thought we could walk over Buffalo, but they are too good of a team for that."