Hoes, a 2008 third-round pick of the Orioles, led off the ninth with a single. Miguel Abreu sacrificed and first baseman Tyler Moore threw the ball into right field. Hoes scored just ahead of Bill Rhinehart's throw.
The Nationals scored eight times in the top of the first, with Jamar Walton belting a grand slam and Robbie Jacobsen adding a solo shot.
The Keys stormed back for seven in the bottom of the inning, capped by Brian Ward's grand slam. The North Division first-half champions tied it in the second on Hoes' RBI groundout, then took the lead in the fifth on a run-scoring single by Pedro Florimon Jr.
Potomac forced extra innings when former fourth-round pick Derek Norris led off the ninth with a home run. He went 2-for-3 with a pair of walks after drawing a league-leading 89 free passes during the regular season.
Frederick starter Oliver Drake did not survive the opening frame and was charged with eight runs on three hits. Cole McCurry restored order by striking out six over 4 1/3 scoreless innings. Will Startup (1-0) got the win, despite giving up a run over 1 2/3 frames.
Ward and Kyle Hudson each collected three hits for the Keys, who host Game 2 on Thursday.
Joe Testa (0-1) was tagged with the loss after he was reached for an unearned run on three hits over 1 1/3 innings.
In other Carolina League action:
Winston-Salem Dash 3, Kinston Indians 2
Jason Bour broke a sixth-inning tie with an RBI single and Hector Santiago and Tyson Corley combined for 3 1/3 innings of scoreless relief for Winston-Salem. Chun-Hsiu Chen and Donnie Webb each had two hits and drove in a run for the Indians. Box score