Millas will start at catcher and bat eighth Wednesday against the Cardinals.
Keibert Ruiz was expected to open the season as the Nationals' clear No. 1 catcher, but he's instead been part of a timeshare at the position with Millas. The two backstops have alternated starts through Washington's first 12 games, but neither has separated himself from the other from a performance standpoint. Millas has maintained a .509 OPS through 21 plate appearances, while Ruiz owns a .563 OPS over 22 plate appearances.