Jared Beach made it 2-0 with 13 minutes left in regulation. Pieper took a corner kick that Abel Clark headed over to Beach, who one-timed it into the goal.
The Warriors (5-7. 3-4) travel to Sidney today.
Windham 6, Jefferson 1
Russ Pelham scored three goals for Windham, which won on the road in the Delaware League.
Anthony Savasta, Malcolm Seamans and Zach Meyer also scored the Warriors, who had a 6-0 lead before Nick Smith scored for winless Jefferson.
The J-Hawks will finish their season Friday at Stamford.