Keselowski passed defending champion Kyle Busch with 75 laps to go and held off Busch's teammate, Darrell Wallace Jr., in the UNOH 200.
Wallace closed to Keselowski's back bumper with two laps left, but drifted high in turn 1 and Keselowski pulled away.
Four-time truck series champion Ron Hornaday Jr. finished third, followed by Matt Crafton and series points leader Johnny Sauter. Busch crashed with 22 laps left and finished 24th.
Keselowski's first truck series win came after 62 starts. The driver of the No. 19 Ford is the 25th driver to win in all three of NASCAR's national series: Sprint Cup, Nationwide and trucks.
Rain washed out the race on Wednesday night.