Sweden born Ghanaian forward Robin Quaison also came off the bench to score as the 05'ers thrashed the Regional League side 5-1.
Issah, who was returning from an impressive loan spell at FC Utrecht, was given a starting role.
But the Bundesliga side fell to an early lead to the home side, when Noah Plume grabbed the opener after 17 minutes.
However, after many attempts in the first half, Mainz went into the break a goal down.
Jean-Philippe Mateta then grabbed an equalizer for the visitors shortly after the break.
Issah Abass was replaced three minutes after the equalizer before Adam Szalai shot Mainz into the lead.
Mateta netted his second of the game, as Robin Quaison put the game beyond Havelse with the fourth goal of the game.
Mateta completed his hat-trick with the final goal of the game in the 90th minute. Read Full Story
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