Marchand earned the penalty shot by stealing Rasmus Ristolainen's pass near the Buffalo blue line and gaining the zone with speed. Ristolainen dropped his stick and grabbed Marchand to prevent a scoring chance. It was the first overtime penalty-shot goal in Bruins history.
"To be honest, I was so tired so I was just trying to catch my breath going in there," Marchand said. "So I was trying to read what he was doing and luckily it went in."
Loui Eriksson also scored for Boston, which is 7-2-1 in its past 10 games.
"The third period, it's a 1-1 hockey game. ... the team we've been playing here deserves a lot more credit for how they're playing because they're a hard team to play against," Bruins coach Claude Julien said. "It was a good pace to the game. Even the referees were mentioning how quick of a pace of a game that was, back and forth. And I thought we battled hard, both teams did. And at the end, it took an overtime win to decide the outcome. So I like the way our guys are competing right now and just by working the way we have and committing a little bit more we're only going to get better."
Sam Reinhart scored for the second straight game and Robin Lehner made 36 saves for the Sabres (21-26-6), who haven't lost in regulation in the past four games (2-0-2).