Alvarez will start Friday's game against the Padres, Kyle Williams of TheBanner.com reports.
He's taking the rotation spot vacated by the injured Jake Irvin (shoulder). Alvarez has been terrific in a long-relief role so far for the Nationals, contributing a 2.84 ERA and 16:3 K:BB over 12.2 innings. The left-hander hasn't thrown more than 56 pitches in any of his relief outings this month but exceeded 90 pitches on two occasions at Triple-A Rochester in early May, so Alvarez should be capable of providing some length.