The Hawks (4-3), who trailed 22-20 at halftime, used a 15-1 run to open a 14-point lead, 42-28, with 8:16 remaining, but the Crusaders (4-4) came back.
Jordan Stevens' 3-pointer capped a 17-4 run that cut Hartford's lead to 46-45 with 17.8 seconds left. Cooper was fouled by Dave Dudzinski and made both shots to increase the lead to three. Justin Burrell missed a 3-point try for Holy Cross at the buzzer.
Both teams struggled with their shooting. Hartford shot 31.5 percent (17 of 54), while the Crusaders made 35.3 percent (18 of 51) but just 2 of 17 3-point attempts.
Dudzinski scored 13 points and grabbed 15 rebounds for Holy Cross, which had a 43-28 edge on the boards.