Blackburn started the 2010 season relatively strong, going 6-1 in April and May, with a 4.28 ERA. However, he struggled after that, going 1-6 with a 9.20 ERA over his next nine starts. On July 21, 2010, Blackburn was demoted to the bullpen and replaced in the rotation by Brian Duensing. In one relief appearance, Blackburn surrendered three earned runs in two innings. Through July 29, Blackburn was 7-7 with a 6.66 ERA.
On July 29, the Twins optioned Blackburn to triple-A Rochester to make room on the active roster for newly acquired closer Matt Capps. He was recalled on August 21, 2010, after Kevin Slowey was placed on the 15-day disabled list with a triceps injury.