Bergeron set up Pastrnak for a one-time slap shot to give Boston a 1-0 lead 3:15 into the second period, then added another helper on Marchand's winner just 28 second into overtime.
Also returning from injury for Sunday night's game was defenseman Torey Krug, who missed the previous two games with an upper-body injury. It was Krug's billiards pass off the left boards that sent Marchand away for the game-winner.
Bergeron, whose right foot was fractured Feb. 24 against Toronto, has 27 goals and 29 assists in 55 games. Krug has a career-best 53 points (13 goals, 40 assists).
The rest of the injured Bruins remained back in Boston -- defensemen Charlie McAvoy and Zdeno Chara (upper body); and forwards David Backes (leg), Jake DeDrusk (upper body) and Rick Nash (upper body) -- with the team headed to Winnipeg for Tuesday's wrap-up of the four-game road trip.
The Bruins, who went 9-2-2 in Bergeron's absence, are now just two points behind Tampa Bay for the top spot in the Eastern Conference after Sunday night's victory. The two teams meet in Boston Thursday night.