The Sabres forced overtime with 26.6 seconds left when Cody Hodgson scored his 14th goal of the season, tipping in Thomas Vanek's pass into the slot during a power play.
Boston still clinched a playoff berth by gaining one point. The Bruins are tied in points with Montreal atop the Northeast Division, but have one game in hand on the Canadiens. Both teams trail Eastern Conference-leading Pittsburgh by nine points.
There was heightened security at TD Garden where cars entering the garage were searched, and fans were checked with wands and patted down.
There was a pregame period of silence and a slideshow of scenes from the Boston Marathon in which three people died and more than 170 were wounded when two bombs went off near the finish line on Monday.
Vanek also scored in regulation for Buffalo. Daniel Paille and Chris Kelly both gave Boston one-goal leads that the Bruins failed to hold.
The 10th-place Sabres are two places and two points below the Eastern Conference's post-season cutoff, but have only four games to go.
PENGUINS 6, CANADIENS 4
PITTSBURGH (AP) — Brenden Morrow scored two goals for the second straight game and Pittsburgh beat Montreal to move closer to clinching the top seed in the Eastern Conference playoffs.
The Penguins lead the Canadiens by nine points in the fight for the top seed. Both teams have five games remaining.
Brandon Sutter added two goals for Pittsburgh, and newly acquired Jarome Iginla and Doug Murray also scored for the Penguins, who had little trouble with the Canadiens despite playing without injured stars Sidney Crosby (broken jaw) and Evgeni Malkin (shoulder).
Marc-Andre Fleury stopped 31 shots, and Pittsburgh dominated in racing to a quick 4-0 lead.
Brian Gionta, Alex Galchenyuk, Gabriel Dumont and Andrei Markov scored for the reeling Canadiens, who have lost three straight. Peter Budaj started in goal but was pulled after stopping just six of the nine shots he faced in the first period.
Carey Price relieved and allowed three goals on 20 shots, absorbing the loss.
BLUE JACKETS 3, DUCKS 2, OT
ANAHEIM, Calif. (AP) — Fedor Tyutin scored 2:19 into overtime, and Columbus won its fifth straight game and moved into eighth place in the Western Conference with a victory over Anaheim.
Blake Comeau and Matt Calvert also scored for the Blue Jackets, who rallied to win and jumped two points ahead of Detroit. Columbus moved within one point of seventh-place St. Louis, which has two games in hand. Sergei Bobrovsky made 26 saves.
The Ducks, who already have clinched a post-season berth, lead Los Angeles and San Jose by seven points in their bid for their second Pacific Division title.
Defenceman Sami Vatanen scored his first NHL goal, one day after Anaheim recalled him from the minors, and David Steckel ended a 32-game goal drought. Viktor Fasth stopped 25 shots.
FLAMES 3, RED WINGS 2
CALGARY, Alberta (AP) — Steve Begin scored two goals in the third period, and Calgary held on to hand playoff-hopeful Detroit a one-goal loss. Begin took advantage of a pair of blunders by goalie Jimmy Howard to score his third and fourth goals of the season.
Lee Stempniak also scored for the Flames (17-22-4), who won all three games against the Red Wings this season.
Gustav Nyquist and Johan Franzen scored for the Red Wings (20-16-7), who are 2-2-2 in their past six games. Detroit dropped to ninth place in the Western Conference, two points behind Columbus and the post-season cutoff.
Miikka Kiprusoff made 36 saves to earn his first win since he topped St. Louis on March 24. Howard, who signed a six-year, $31.8 million contract on Tuesday, stopped 14 shots.