The Seahawks (13-11, 7-4 Northeast Conference) moved within a game of the second-place Bulldogs (16-10, 8-3).
Wagner used a 9-0 run in the first half and Bryant never got closer than seven the rest of the way. The Seahawks led 34-24 at the half.
The last time Bryant got within seven was on a Joe O'Shea 3-pointer with 3:31 left to play. Rivers promptly responded with a three-point play. Then the Seahawks made 11 of 12 free throws in the final 2:03.
Marcus Burton added 13 points for Wagner.
Alex Francis kept Bryant in the game with 26 points and 10 rebounds. He became the sixth player in league history and fourth Bulldog to surpass 2,000 points.
Wagner hit 8 of 16 3-pointers and 21 of 26 free throws.