After Alex Lyon made the save on a Zdeno Chara slap shot, David Pastrnak took a couple whacks at the rebound before Marchand scored the winner for the third straight game.
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"A little easier," Marchand said of the goal compared to those he scored in overtime in a 6-5 win against the Detroit Red Wings on Tuesday and in a 2-1 victory against the Montreal Canadiens on Saturday. "But I think it's just a product of everybody doing their job the right way and keeping it simple, and when you do that, get pucks to the net, good things happen."
Riley Nash and Brian Gionta scored, Chara and Pastrnak each had two assists, and Tuukka Rask made 31 saves for the Bruins, who matched a season-high with their fifth win in a row.
Boston (42-15-8) trails the Tampa Bay Lightning by six points for first place in the Atlantic Division and leads the Toronto Maple Leafs by seven for second. It has three games in hand on Tampa Bay and Toronto.
The Bruins have played five straight games without center Patrice Bergeron (fractured foot) and the past two without defenseman Charlie McAvoy (sprained MCL). Forward David Backes served the first of a three-game suspension for interference against Red Wings forward Frans Nielsen.
"It shows the depth when you have some big guys out of the lineup," Gionta said. "We're still able to find ways to win, and for sure, we have some big guys, big pieces that are out of the lineup right now."
Jakub Voracek and Jori Lehtera scored, and Lyon made 24 saves for the Flyers, who have lost five in a row (0-4-1).