Selman dropped to 7-6 despite giving up just two runs (one earned) and four hits in five innings of work.
Michael Ohlman's 5th inning home run to left field, his 8th of the season, broke the 1-1 tie and proved to be the difference in the contest.
Ohlman earlier gave the Keys a 1-0 advantage on an RBI single in the bottom of the 3rd inning, only to have Lane Adams tie the game for Wilmington in the next half inning.
Otherwise the Blue Rocks could not get to Frederick starter Tim Berry, who pitched eight 3-hit innings, striking out 7 while improving to 7-4 on the season. David Walters struck out two during a perfect 9th inning for his 9th save.
The loss kept Wilmington from sweeping the series, the Blue Rocks open up a four-game series in Potomac Thursday night.
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