After winning the first game of their playoff series with Potomac on Wednesday, Frederick lost the last three games of this series and the Keys season ended with tonight's 10-3 loss at Potomac.
The Nationals advance to face Winston-Salem for the Carolina League championship after taking the series, three wins to one.
Frederick starter Luis Noel gave up four runs over 2 2/3 and Keys starters allowed 17 earned runs over 11 1/3 in the series.
Ronnie Welty hit a solo homer and Tyler Townsend had three hits, including a two-run double for Frederick.
Potomac scored two runs in the 2nd and 3rd and three runs in the 4th and 7th frames in the victory.