Blach was recalled from Triple-A Sacramento on Monday, Kerry Crowley of The San Jose Mercury News reports.
Blach was promoted to the major leagues after Derek Holland (finger) was moved to the 10-day injured list. Blach made 13 starts in 2018 for San Francisco and posted a 4.25 ERA with 75 strikeouts over 118.2 innings, though it's unclear if he'll be used as a starter or a reliever during his time in the big leagues.