The game-deciding goal came in the 104th minute from Mount Union's Cortni Arp, cementing the Raiders 2-1 victory.
Only two goals were scored in regulation time, with each side netting one apiece to force the overtime frame.
The Terriers struck first with sophomore Kaitlyn Harris ripping a shot past the Raiders keeper to help Hiram take the lead in the 27th minute.
The rest of the half was a silent one with each side trading shots.
The scoring action resumed in the 89th minute when Mount Union's Lauren Beech scored the first Raider goal of the night.
In the last three minutes of regulation, Hiram totaled four shots with neither finding the back of the net. Junior Hannah Ward, sophomore Kaitlyn Harris, junior Courtney Wendel, and freshman Emily Kazimore each tallied a shot apiece sending the game into overtime.
In goal, senior Ally Green tallied 14 saves in 103 minutes of work.
Hiram finished with 13 shots on goal and a 10-8 edge in corner kicks.
The Terriers will return to the field on Saturday, Sept.28 when they enter conference play against Wittenberg. The matchup with the Tigers is set for 4:00 pm.