Alonzo Breitenstein (November 9, 1857 – June 19, 1932) was a National League pitcher. Breitenstein played for the Philadelphia Quakers in the 1883 season. In one career game, he had a 0-1 record with a 9.00 ERA. Breitenstein allowed nine runs on eight hits, in 5.0 innings pitched. With what hand he batted and threw is unknown.