The Seahawks (21-4, 12-2 Northeast Conference) led 18-12 with 12:09 to go in the first half before scoring 10 straight. Rivers sandwiched the run with a 3-pointer and a jumper.
Wagner shot 55.2 percent (16 of 29) in first half, going 5 of 10 from 3-point range and got 13 points from Rivers.
Rivers finished with 15 points and Tyler Murray and Chris Martin chipped in 11 each for the Seahawks.
Wagner shot 53.2 percent for the game (16 of 29) as Williams led the way, shooting 7 of 10.
Wagner pushed its lead to as many as 24 twice in the second half, and scored 29 points off 18 turnovers.
Monmouth (9-19, 7-8) was led by Chad Holley with 12 points.