Harper is 4 for 7 in the series with Miami and has looked more comfortable at the plate.
The right fielder said his ankle was more sore and swollen than he expected in the morning but hopes to miss only one game.
Stephen Strasburg vs. Henderson Alvarez.
Jayson Werth is out of the lineup the day after spraining his right ankle.
Matt Williams made a handful of decisions that exposed the roles and quirks of the bullpen.
Nats prospect Austin Voth will make his Class AA debut Tuesday night, barely a month after his last promotion.
The Nationals starter pitched more like himself Monday, firing seven solid innings in his second start back from a bicep injury.
Nationals right fielder Jayson Werth says he hopes to play Tuesday, but that will depend on how his ankle feels in the morning.
Matt Williams wants to play the matchups and the hot hand, and it could be Danny Espinosa, Kevin Frandsen or Zach Walters at second.
Jordan Zimmermann vs. Nathan Eovaldi.