Williams was 9 of 13 from the field and 8 of 10 from the charity stripe as Wagner hit 13 of 17 free throws.
Bryant led 47-44 after Frankie Dobbs sank two free throws. However, Wagner (24-4, 15-2 Northeast Conference) used a 29-7 run, capped off by two Williams free throws, to take a 65-54 lead with 10:47 left to play.
Wagner pushed its lead to 15, 80-65, behind a Kenneth Ortiz jumper. Ortiz finished with 17 for the Seahawks.
Wagner forced 18 turnovers by Bryant (2-27, 1-16) and scored 23 points off those errors. The Seahawks also grabbed 18 offensive rebounds en route to 20 second-chance points.
Alex Francis led Bryant with 21 points and Dobbs had 20, but the Bulldogs were outscored 44-26 in the paint.