In the fourth inning, Rosa singled home Reynaldo Rivera before Kody Clemens scored two on a single giving the Whitecaps a 4-2 lead.
However, the Cougar offense responded with five runs in the fifth inning to take a 7-4 lead.
The final Whitecaps run came in the eighth inning when Brady Policelli scored on a Kane County error.
Policelli, Deatherage and Rosa all led the Whitecaps offense with two hits on Thursday night while Clemens and Rivera each had two RBIs.
The Whitecaps fall to 48-49 overall on the year and 12-15 in the second half, six games behind Bowling Green for first place in the Midwest League Eastern Division second half standings.