Interleague play
Kansas City began Interleague play against their cross-state rival St. Louis Cardinals. After losing the first two games of the series by scores of 5–0, the Royals fell to a 21-22 record and under the .500 mark for the first time since April 11 when they were 2-3. After optioning three players (Mike Avilés, Luke Hochevar, and Robinson Tejeda) to the inactive roster, Kansas City won the final game 3–2 and regained a .500 record on the season.