Sandy Leon got the Nationals (14-22) on the board in the second inning, with some help from Steven Souza's speed. After Souza walked with one out, he stole first base when Matusz paid him no mind. After J.P. Ramirez flied out to center for the second out, Souza also took off with a 1-2 pitch to Leon. Leon lined it to left field, scoring Souza and staking the Nats to a 1-0 lead.
Matusz, the Orioles' ace, made his first rehab start recovering from a ribcage injury. He went four innings, threw the prescribed 60 pitches, and found a nice groove. He allowed one earned run on two hits, with a pair of strikeouts and two walks.
Holder breezed through seven innings, needing just 73 pitches to retire the Keys (21-15) and keep them off the board. But things turned against him in the eighth. A leadoff infield single by Tyler Kolody started the rally. After Miguel Abreu flied to center for the first out, Dale Mollenhaur singled to center. Brian Ward struck out to get Holder an out away from escape, but pinch hitter Jacob Julius laced a single to left to tie the game.
Holder then struck out Steve Bumbry, but the baseball made its way to the backstop. Bumbry reached to load the bases and extend the inning. Buck Britton then singled to left to score a pair and give the Keys a 3-1 lead.
Potomac rallied in the ninth with another RBI single from Leon. The Nats had runners at the corners with two outs but Jose Lozada struck out swinging to end the threat.
With the victory, the Division-leading Keys stretch their lead to seven games over Potomac.
The clubs continue the series Tuesday night at Harry Grove Stadium. Paul Demny takes the hill for Potomac against Nathan Moreau at 7 P.M.