Guerrero, a 23-year-old left-hander, was named the Sox's minor-league pitcher of the month for June after he went 4-0 with a 1.23 ERA, four walks, 26 strikeouts, a shutout and a .195 opponents' average over five starts. Guerrero has allowed two or fewer runs in each of his last six starts, throwing at least six innings in five of them.