Castillo (0-1) took the loss against Tampa Bay on Thursday, pitching five innings and allowing one run on three hits and one walk while striking out three batters.
Castillo was sent to the minors after the Royals acquired him in a trade with Toronto on Aug. 2, but he made only two starts before Kansas City called him up. Though he took the loss Thursday, the right-hander pitched well, throwing 48 of 69 pitches for strikes and keeping the Rays off the scoreboard after Yandy Diaz tagged him for a leadoff homer in the first inning. Given his success in the outing, Castillo will likely get more turns in the rotation for a Kansas City team that is already looking ahead to next season.