He played for the Washington Senators and Boston Braves (both of the National League), and the Boston Red Sox and St. Louis Browns of the American League. Dinneen recorded three wins for the Red Sox over the Pittsburgh Pirates in the first World Series in 1903. Dinneen broke the record for most strikeouts in a World Series game with 11; the previous mark of 10 had been set a day earlier by Pittsburgh's Deacon Phillippe.