The Whitecaps took a 3-2 lead in the top of the fifth when Jordan Pearce scored on a Fort Wayne error and Luke Burch brough hope Cole Peterson on an RBI single.
In the bottom of the fifth, Fort Wayne scored five runs, taking a 7-3 lead that ended up being the final score.
Overall, Burch led the Whitecaps with four hits and an RBI while Rosa also had an RBI.
The Whitecaps fall to 20-19 overall on the season and sit in third place in the Midwest League Eastern Division, 6 and ½ games behind first place Lansing.
West Michigan will return home on Friday to begin a series with Lake County, beginning at 7:05 p.m.