Cy Young wins the 500th game of his career as the Cleveland Naps beat the Washington Senators, 5 – 4, in 11 innings. He is the only pitcher in major league history to ever reach this milestone.

On May 19, 1910 — Cy Young wins the 500th game of his career as the Cleveland Naps beat the Washington Senators, 5 – 4, in 11 innings. He is the only pitcher in major league history to ever reach this milestone.

Source:
Baseball Reference May 19