Pastrnak had two goals and two assists, Bergeron added a goal and two assists and the Bruins beat the Ottawa Senators 4-1 on Tuesday night.
The Bruins (5-2-2) snapped a three-game skid and beat the Senators for the second time this season. David Krejci scored his second of the season, and Rask made 38 saves.
Rask had allowed 14 goals in his first four starts this season.
''Tuukka gave us the saves we needed, for his own self as well,'' Bruins coach Bruce Cassidy said.
Thomas Chabot scored the lone goal for the Senators (4-3-1), who ended a three-game winning streak to wrap a season high five-game homestand with a 3-2-0 record as they depart for a three-game trip Thursday.
''We had 39 shots against a good team like that means we did enough to score some goals, but their goalie was very good,'' said Senators coach Guy Boucher. ''Maybe we could have had more screens in front of him, we'll look at the video, but when you have 39 shots you have plenty of chances.''
Craig Anderson stopped 28 shots.
Boston made it 3-1 just 21 seconds into the third on the power play. Bergeron tipped Pastrnak's shot, and then put the game out of reach as Brad Marchand dangled his way around Dylan DeMelo and found Pastrnak alone at the side for his second of the night.
''I was kind of looking for (Pastrnak) the whole way, but I didn't see a good lane,'' said Marchand. ''He reached, I teached and luckily it went in.''
Trailing 1-0, the Senators tied it late in the second as Chabot scored a power-play goal from just inside the blue line, but the Bruins quickly regained the lead.
Already shorthanded, the Senators were called for too many men, giving the Bruins a two-man advantage. They scored on their first shot as Krejci beat a sprawled Anderson.
''It was big (to get two points),'' Pastrnak said. ''Even though we had two points on this trip we haven't won and, obviously, every loss feels tough, so good that we (played) hard and got a big win for us.''
NOTES: Senators F Alex Formenton returned to the lineup after missing three games with a concussion. Cody Ceci (upper body), Brady Tkachuk (leg) and Ben Harpur (undisclosed) were still out. ... The Bruins were without Charlie McAvoy (upper body), Kevan Miller (hand), Torey Krug (ankle) and David Backes (undisclosed).
Bruins: Host Philadelphia on Thursday night.
Senators: Play at Colorado on Friday night.
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