Matt Swynenberg (7-5) increased his scoreless inning streak to 14 innings by blanking Carolina (63-74) for six innings. He scattered four hits while striking out five.
Benny Suarez (0-1) took the loss in only his second start for the Mudcats. The right-hander surrendered all three runs to Potomac (62-74) on four hits in the third inning. Rob Wort earned his 13th save after tossing two scoreless innings to finish.
The Nationals had four straight hits to open the scoring in the pivotal stanza. Adrian Sanchez drove in the first run, and was followed by a hit from Matt Skole for a 2-0 lead. A sac-fly by Rick Hague to center drove in the final run of the evening.
Giovanny Urshela extended his hitting streak to 10 with a first inning single.
The Carolina Mudcats finish the regular season with three games at Frederick. The Mudcats and Keys square off at 6 p.m. Saturday night at Harry Grove Stadium. Tickets are available by calling (919) 269-2287 or visiting carolinamudcats.com.