Armstong will serve as the Guardians' opener Monday in Game 6 of the ALCS versus the Rays, Tim Stebbins of MLB.com reports.
It will be the third appearance in as many days for Armstrong, who tossed 1.1 scoreless frames in Game 5 and another scoreless inning in Game 4. He's been lights out this postseason, allowing only two hits with a 6:0 K:BB over 7.2 scoreless frames.