The No. 4 Boston University men’s hockey team defeated its crosstown rival Boston College, 6-3, before 6,150 at Agganis Arena Friday night. BC got on the board first with a power-play goal from Trevor Kuntar at 10:43 of the first period. But the next five goals were all BU’s, including a pair from Ty Gallagher that pushed the lead to 5-1 halfway through the third period. Drew Commesso had 24 saves for BU (18-6-0, 12-4-0 Hockey East), while Mitch Benson had 24 saves for BC (9-8-5, 5-5-4) and Henry Wilder had nine.