Blackburn was sent down to Triple-A Las Vegas on Saturday, Daniel Kramer of MLB.com reports.
Blackburn was just called up from the Aviators on Friday, but his stay with the Athletics was never expected to be long term. The right-hander essentially served as a one-day stand-in for J.B. Wendelken, who couldn't be promoted until Saturday due to the mandatory 10-day waiting period in place for such scenarios. Manager Bob Melvin explained that Blackburn's best chance at seeing consistent game action is on the farm, with the big-league club having much more of a need for relievers than starters at the moment.