Pimentel controls P-Nats
Pimentel (6-3) allowed one run on four hits and three walks while striking out four. The 21-year-old right-hander won his third straight decision and lowered his ERA to 2.48.
Arthur Santos and Russell Haltiwanger each tossed a scoreless frame to close it out.
The Blue Rocks (14-5) broke a 1-1 tie with five runs in the fifth inning. Marc Maddox ripped a two-run triple, Chris McConnell and Brian McFall delivered RBI doubles and Mario Lisson slapped a run-scoring single.
McFall's RBI double in the fourth had tied the game.
Devin Ivany belted a solo homer, his second, in the second for the Nationals (10-9), who had their five-game winning streak snapped.
Potomac starter Cory VanAllen (1-3) surrendered five runs on four hits while fanning seven and walking two in 4 1/3 innings.