Youngstown State took a 76-73 lead with 3:07 left in overtime, but the Crusaders (17-7, 9-3 Horizon League) scored 13 of the next 15 points for their 12th consecutive victory over the Penguins (8-15, 2-11).
Trailing 76-75, Valparaiso's Ryan Broekhoff hit a 3-pointer for a 78-76 lead with 1:53 left in OT. DuShawn Brooks' jumper tied the score at 78, but the Crusaders finished the game on an 8-0 run.
Youngstown State's Kendrick Perry hit a jumper at the buzzer to force overtime.
Broekhoff finished with 11 points and 14 rebounds, Howard Little had 11 points and Matt Kenney added 10 for Valparaiso.
Vytas Sulskis scored 17 points and 10 rebounds, Brooks and Perry had 15 each and Ashen Ward added 11 for Youngstown State.