Clay Holmes made his MLB debut with the Pittsburgh Pirates in 2018. The right-handed pitcher appeared for Pittsburgh on April 6, 2018, beginning a major-league career that later included a move to the New York Yankees.
Holmes was drafted by the Pirates in the ninth round of the 2011 MLB draft out of Slocomb High School in Alabama. He developed as a starting pitcher in Pittsburgh’s farm system before reaching the majors, where he initially worked in a relief role and also made starts during his rookie season.
The 2018 debut date is the key detail: Holmes was not a Pirates debutant in a later season, and his eventual reputation as a Yankees reliever can make the earlier Pittsburgh connection easy to overlook. Pittsburgh traded him to New York in July 2021.
With the Yankees, Holmes became one of baseball’s prominent late-inning relievers and was selected to the American League All-Star team in 2022 and 2024. That later success does not change the answer to the debut question: it was Holmes who first reached MLB with Pittsburgh.