The Monarchs took a 1-0 lead at the 12:43 mark of the opening period when Marc-Andre Cliché tallied his 11th goal of the season. John Zeiler and Jeff Likens recorded the assists.
Manchester scored the final goal of the game at 9:39 of the second period.
Zeiler netted his sixth goal of the season with Richard Petiot picking up the lone assist. Neither team could muster any offense in the final period.
Tuukka Rask stopped 18 of 20 shots for the P-Bruins, and the team went 0-for-5 on the power play but offset that by going 8-for-8 on the penalty kill.
The loss moves the Eastern Conference champions to 54-17-3-4 on the season.
The P-Bruins return to action tonight against the Monarchs at the Verizon Wireless Arena in Manchester at 7:05 p.m. and close out the season tomorrow at The Dunk for a Family Game at 4:05 p.m. against the Lowell Devils.
The Calder Cup playoffs begin Wednesday and continue Friday at The Dunk against the Monarchs; both games are at 7:05 p.m.