Kauffman Stadium fans, treated to video clips of Cook's TV performances on the giant CrownVision board, screamed as he took the field.
Cook, wearing a personalized Royals jersey with No. 08, threw a left-handed low-and-inside pitch to Brett Tomko, a pitcher who crouched behind home plate.
Afterward, manager Trey Hillman presented him a framed duplicate of the Royals' lineup card with Cook listed as the 10th man.
"My performances are always dedicated to the Kansas City Royals," Cook told the crowd.
Cook, from the suburb of Blue Springs, Mo., had a busy day. He gave a concert in Kansas City, appeared at a Blue Springs elementary school and was given a parade in his hometown.
Although plans called for Cook to sing the national anthem before the game, he deferred to the kids' group originally enlisted for that honor, the Southwood Elementary Choir.
Instead Cook sang "Take Me Out to the Ball Game" during the seventh inning.
Waving happily to the fans after the first-pitch ceremony, he declared: "I love you guys. I couldn't do it without you."
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.