The left-handed starter has a 3.00 ERA over his past five starts.
Two first-place teams begin a three-game series with Gio Gonzalez facing Roberto Hernandez.
Gio Gonzalez is winless since July 5, and his pitching coach thinks he needs to throw more curveballs.
The left-hander entered the game with a 5.46 ERA over his previous six outings and fired seven scoreless on Thursday.
The left-handed starter is averaging 5.7 innings per start, his lowest mark since 2009.
Gio Gonzalez spent all day Thursday trying to get back to Washington after the all-star break, and he is pitching a day later than scheduled as a result.
The left-handed starter's fastball was down one to two miles per hour from normal, and he still threw well.
Bryce Harper swung a bat with both hands Tuesday, but his ensuing return probably won't lead to a shakeup.
The outfielder first felt the back discomfort Sunday morning and considers it minor.
The left-handed reliever will be with the Nationals for, at least, the weekend as an extra arm in the bullpen.