Wade Redden scored a power-play goal early in the third period on Thursday as the top-seeded Ottawa Senators beat the Sabres 2-1 and cut Buffalo's lead to 3-1 in the Eastern Conference semifinal series.
Brian Pothier also scored and Ray Emery stopped 29 shots.
Daniel Briere scored for Buffalo, which had a five-game winning streak snapped and lost for the first time in five home playoff games.
The best-of-seven-series shifts to Ottawa for Game 5 today.
The Senators still have a long climb back, considering only two NHL teams -- Toronto in 1942 and the New York Islanders in 1975 -- have rallied from a 3-0 series deficit to win.
Redden's goal came 3 minutes into the third period and shortly after Buffalo's Derek Roy was penalized for tripping.
Mighty Ducks 4, Avalanche 1
At Denver, Todd Marchant, Teemu Selanne and Dustin Penner scored goals and 25-year-old Russian rookie Ilya Bryzgalov was again brilliant in goal for Anaheim, which completed a four-game sweep of Colorado and advanced to the Western Conference finals for the second time in three seasons.
Bryzgalov stopped 40 shots, capping a dazzling series that included two wins on the road after his shutout streak was snapped at three games and just shy of 250 minutes, the longest by a rookie and second best in NHL playoff history.
Anaheim, which stifled Colorado's Fab Four of Joe Sakic, Alex Tanguay, Milan Hejduk and Andrew Brunette all series long, handed the Avs their first sweep in 26 playoff series since they arrived from Quebec before the 1995-1996 season.
The Ducks stretched their streak to 36 consecutive penalties killed by turning away all five of Colorado's power plays. The Avs finished 0-for-24 on the power play in the series and ended the season in an 0-for-33 slump over six games.
Sakic gave Colorado a 1-0 just 2:17 after the opening faceoff.
Anaheim will face San Jose or Edmonton for the right to represent the West in the Stanley Cup finals.
Canada trounced Latvia 11-0 on Thursday in both teams' second-round opener, a game suspended twice because of fans throwing debris onto the ice in anger over American referee Rick Looker.
Fans disrupted the game by throwing 17 lats (US$31) worth of coins on to the ice in the first period, when Looker called eight penalties against Latvia, four resulting in power-play goals for Canada.
Early in the third period, Latvian forward Janis Sprukts urged calm over the arena's public address system, enabling the game to continue. Canada went on to score three more goals, two on power plays to give Canada nine for the game. No coins were thrown on the ice later in the third period.
"You have to think about the players' safety," Canadian head coach Marc Habscheid said. ``Latvia's great fans ... they're very passionate fans about their team. There were just a few people that decided to throw things on the ice.
"It made it dangerous for the players, but we have a lot of respect for the Latvian team and the Latvian fans. It's not fair to look at all the people in the stands."
Earlier, Maxim Sushinsky had two power-plays goals and an assist, and Russia routed Ukraine 6-0 to also stay unbeaten.
Earlier this season, Looker was heavily criticized after Cologne beat Dusseldorf in the semifinals of the German League playoffs. He assessed a five-minute major to a Cologne player at the end of the game. Dusseldorf scored three goals and won the game.