Thomas has been suffering with a dead-leg but will now take his place amongst the replacements alongside Scarlet Rob McCusker, with them both providing second and back row cover.
Wasps back row Andy Powell is the player, from the three named to fill two replacement positions last Tuesday, who misses out on this occasion.
Wales: L Byrne (Ospreys); L Halfpenny (Cardiff Blues), J Roberts (Cardiff Blues), J Davies (Scarlets), S Williams (Ospreys); J Hook (Ospreys), M Phillips (Ospreys); P James (Ospreys), M Rees (Scarlets, capt), C Mitchell (Ospreys), B Davies (Cardiff Blues), A-W Jones (Ospreys), D Lydiate (Newport Gwent Dragons), S Warburton (Cardiff Blues), R Jones (Ospreys).
Replacements: R Hibbard (Ospreys), J Yapp (Cardiff Blues), J Thomas (Ospreys), R McCusker, D Peel (Sale Sharks), S Jones (Scarlets), M Stoddart (Scarlets).
Ireland: L Fitzgerald (Leinster); T Bowe (Ospreys), B O’Driscoll (Leinster, capt), G D’Arcy (Leinster), K Earls (Munster); R O’Gara (Munster), E Reddan (Leinster); C Healy (Leinster), R Best (Ulster), M Ross (Leinster), D O’Callaghan (Munster), P O’Connell (Munster), S O’Brien (Leinster), D Wallace (Munster), J Heaslip (Leinster).
Replacements: S Cronin (Connacht), T Court (Ulster), L Cullen (Leinster), D Leamy (Munster), P Stringer (Munster), J Sexton (Leinster), P Wallace (Ulster).
