Jayson Werth will DH and Nate Schierholtz plays left field against Felix Hernandez behind Jordan Zimmermann.
The Nationals extended their player development contracts with both minor league affiliates for two more years.
The Nationals have never faced Felix Hernandez, but they'll get their first look tonight in Seattle.
Nationals shortstop prospect Wilmer Difo was named the South Atlantic League MVP.
Only five starters in baseball have yet to allow a stolen bases and Fister is among them.
Since 2012, the Nationals are 11-17 at Citizens Bank Park, including 3-6 this season.
Three times over the past two losses, the Nationals have failed to move a runner over from second base.
Adam LaRoche has dealt with back stiffness for years and knows his recent bout isn't serious.
Doug Fister will try to prevent the Phillies and Kyle Kendrick from sweeping the Nats.
Adam LaRoche is back in the lineup after nursing a stiff back on Tuesday.