Petrie connected on 4 of 6 attempts from beyond the arc for the Polar Bears (2-1), who shot 11 of 26 (42.3 percent) overall from three-point land.
Senior Mark Yakavonis (Barrington, R.I.) contributed 12 points, 17 rebounds (10 offensive) and three blocks to the win, while sophomore Kevin Bradley (Seekonk, Mass.) added 15 points.
Bowdoin, which held a 51-36 rebounding advantage, outscored the Nor'easters 17-7 over the final 3:40 to gradually pull away. The Polar Bears led 37-30 at the half.
Junior Matt McManus (Cumberland, R.I.) tallied a game-high 20 points for the Nor'easters, who lost for the first time in three outings. Sophomore Tom Button (Lyndeborough, N.H.) added 10 points to go with seven rebounds.
Both teams are off until after Thanksgiving break. The Polar Bears host Southern Maine on November 30, and the Nor'easters entertain Daniel Webster College on December 2.