Blackburn was recalled from Triple-A Las Vegas on Friday, Martin Gallegos of MLB.com reports.
Blackburn has been exclusively a starter this season, posting a 5.26 ERA in 15 starts for Las Vegas and allowing five runs in one three-inning start for Oakland. He appears to be up as a reliever this time around with no gaps available in the big-league rotation before the All-Star break. Tanner Anderson was sent down in a corresponding move.