Washington's free throws capped the scoring for the Peacocks (9-9, 3-4 Metro Atlantic) with a three-point lead. Justin Robinson pulled Monmouth (8-9, 5-2) within 62-61 on a pair of free throws with 52 seconds left.
Robinson's steal with 29 seconds left set the Hawks up with a final shot to win, but Andrew Nicholas' jumper was off in the final seconds.
Robinson scored 22 and Nicholas 17 to lead the Hawks.
Washington made it 50-42 on a jumper with 3:19 left in regulation. The Hawks answered with a 10-2 run to force overtime.
Saint Peter's opened the game missing its first 12 field goals and Monmouth started 2 of 10 from the field. The Hawks led just 6-3 with 10 minutes left in the first half.