Liam Williams and Dan Biggar will miss Wales' final Rugby World Cup warm-up against reigning champions South Africa on Saturday.Both players had been selected to start the match in Cardiff, but have been withdrawn as a precautionary measure.The Welsh Rugby Union said Thursday that full-back Williams had a tight hamstring, with fly-half Biggar suffering from back irritation.Cai Evans comes off the bench to make his Test debut as Williams's replacement, with Sam Costelow replacing Biggar at stand-off.Evans's position among the replacements is filled by Scarlets back Tom Rogers. Revised Wales team 15 Cai Evans; 14 Alex Cuthbert, 13 Mason Grady, 12 Johnny Williams, 11 Rio Dyer; 10 Sam Costelow, 9 Kieran Hardy; 8 Aaron Wainwright, 7 Jac Morgan (captain), 6 Dan Lydiate; 5 Will Rowlands, 4 Ben Carter; 3 Keiron Assiratti, 2 Elliot Dee, 1 Corey DomachowskiSubstitutes: 16 Sam Parry, 17 Nicky Smith, 18 Henry Thomas, 19 Teddy Williams, 20 Taine Basham, 21 Tomos Williams, 22 Max Llewellyn, 23 Tom Rogers South Africa 15 Willie le Roux, 14 Canan Moodie, 13 Jesse Kriel, 12 Damian de Allende, 11 Cheslin Kolbe, 10 Manie Libbok, 9 Jaden Hendrikse, 8 Jasper Wiese, 7 Pieter-Steph du Toit, 6 Siya Kolisi (captain), 5 RG Snyman, 4 Jean Kleyn, 3 Frans Malherbe, 2 Malcolm Marx, 1 Steven KitshoffSubstitutes: 16 Bongi Mbonambi, 17 Ox Nche, 18 Vincent Koch, 19 Franco Mostert, 20 Marco van Staden, 21 Duane Vermeulen, 22 Grant Williams, 23 Damian Willemse