Holmes (triceps) was activated from the 10-day injured list Sunday.
Holmes was knocked around for three runs on four hits over two innings in his first rehab appearance with Double-A Altoona on Aug. 5, but he bounced back Thursday, throwing two scoreless innings with three strikeouts. He will slot back into a multi-inning, low-leverage role out of the Pittsburgh bullpen. Parker Markel was optioned to Triple-A Indianapolis in a corresponding move.