Shemansky scored his first of the night at 8:52 to tie the game, 1-1.
Kyle Beattie gave Maine a 2-1 lead 2:19 into the second period with his third goal of the season.
The Eagles knotted the score with 4:12 remaining in the second period. Barry Almeida struck on the power play for his 11th goal of the season.
Defenseman Brian Dumoulin, who also had two assists, scored 4:03 into the third to give BC the lead.
Shemanksy struck again with 5:11 left in the third, beating Chris Venti (29 saves) with 18 seconds left on a two-man advantage. The forward’s second of the night eventually sent the game into overtime, where Mangene’s slap shot from the slot gave Maine the victory.
UMass-Lowell 4, Northeastern 0 - Scott Wilson scored twice and Derek Arnold and Daniel Furlong had one apiece as the No. 14 River Hawks (13-6-0, 8-5-0 Hockey East) blanked the Huskies (8-10-3, 4-10-2) at the Tsongas Center. Doug Carr stopped 28 shots for the shutout.
UNH 2, Merrimack 1 - Grayson Downing and Stevie Moses scored 28 seconds apart in the first period and the Wildcats (9-11-2, 6-8-1 Hockey East) held off the sixth-ranked Warriors (12-5-5, 8-4-3) in Durham, N.H.
Casey DeSmith had 24 saves to pick up the win. Ryan Flanigan scored and Joe Cannata made 31 saves for Merrimack.
UMass 4, Vermont 3 - Daniel Hobbs had his first career hat trick and Conor Allen’s sixth of the year broke a tie with 3:44 left to give the Minutemen (9-8-5, 5-6-4 Hockey East) the victory over the last-place Catamounts (5-17-1, 2-13-1) at Mullins Center.
Harvard 2, Colgate 2 - Marshall Everson had a goal and an assist, Peter Starrett scored his first collegiate goal, and Steve Michalek matched a career high with 34 saves as the Crimson (4-6-7, 3-4-5 ECAC) tied the No. 18 Raiders (12-8-3, 6-4-1) in Hamilton, N.Y.
Cornell 4, Dartmouth 3 - Cole Bardreau scored a power-play goal 2:05 into overtime, and the No. 9 Big Red (11-4-3, 8-1-2 ECAC) held their first-place spot in the league with a win over the visiting Big Green (7-8-2, 4-5-1).
Doug Jones and Eric Neiley struck on the power play and Mark Goggin also scored for Dartmouth.