The Nationals recalled Cornelio from Triple-A Rochester on Monday.
Cornelio has been shaky in three appearances for the Nationals this season, logging a 6.48 ERA and 4:9 K:BB over 8.1 innings. Though most of the 26-year-old's pro experience is as a starting pitcher, he pitched in a relief role with Rochester after being sent down by the Nationals earlier this month, and he appears ticketed for the bullpen during this stint in the majors.