David Murphy hit a walk-off single off Henry Rodriguez as the Nationals lost their second consecutive game.
The Nationals received bad news about the young closer who had a setback in his recovery from elbow soreness.
Unable to drive the ball with any authority last year while battling a shoulder tear, Nationals first baseman Adam LaRoche has already clubbed two home runs in three games.
Making his first Triple-A start since 2007, John Lannan had a day to forget against the ScrantonWilkes-Barre Yankees.
After squandering Jordan Zimmermann's pitching gem on Sunday, the Nationals realize they're going to have to start producing earlier in ballgames.