Ernest Guy Diehl (October 2, 1877 – November 6, 1958) was a Major League Baseball outfielder who played for four seasons. He played for the Pittsburgh Pirates from 1903 to 1904, and the Boston Beaneaters/Doves in 1906 and 1909. Diehl served as the head baseball coach at the University of Cincinnati in 1910. Diehl also played tennis. At the tournament now known as the Cincinnati Masters he: