Tyler Randell and Jamie Arniel scored 16 seconds apart in the third period to break a 2-2 tie, giving the Bruins the victory. Mike Hoffman
's shorthanded goal brought the Senators within one but Boston goaltender Michael Hutchinson, who made 47 saves, held off Ottawa the rest of the way.
Keegan Dansereau, with his third goal in two games, and Ottawa native Jason Bailey scored in the first period for the Senators, who held a 50-25 edge in shots. Arniel and Jordan Knacksted also scored for the Bruins in the first period.
Shane Connelly turned aside 21 shots in the Ottawa net.
The Senators wrap up play in the rookie tournament on Thursday night, facing off against the host Toronto Maple Leafs. It's a 7 p.m. start, with Rogers 22 providing television coverage.