The second half was all Wales. Just two minutes into the second period Wales fullback Daniel Evans crossed for an unconverted try. Halfpenny added two penalties before late Wales tries from Ryan Bevinton and Rhys Webb put the result beyond doubt.
Ireland did cross in the dying minutes for a consolation score, but it was too little, too late. Wales now play England on Friday.
U18 Home Nations Championship
Wales 35 Ireland 14
Wales U18: Daniel Evans (Amman Valley/Scarlets); James Egan (Whitchurch/Blues), Jason Tovey (Cwmcarn/Dragons), Rhys Williams (Coleg Sir Gar/Scarlets), Leigh Halfpenny (Swansea College/Ospreys); James Thomas (Radyr/Blues), Rhys Webb (Brynteg/Ospreys); Ryan Bevington (Porthcawl/Ospreys), Huw Dowden (Tonyrefail/Blues), Scott Andrews (Y Pant/Blues), Hadyn Pugh (Coleg Sir Gar/Scarlets), Kyle Maiden (Pencoed College/Ospreys), Haloti Molitika (Brynteg/Ospreys), Nick Cudd (Coleg Sir Gar/Scarlets), Sam Warburton (Whitchurch/Blues, Captain)
Replacements from: Patrick Palmer (Y Pant/Blues), Ricky Guest (Coleg Sir Gar/Scarlets), Phil Price (Brynteg/Ospreys), Lee Sims (Brynteg/Ospreys), Gareth Williams (Colstons/Blues), Phil Williams (Whitchurch/Blues), Matthew Lemon (Maes yr Yrfa/Scarlets), Jevon Groves (Y Pant/Blues), Nick Harwood (Bonymaen/Ospreys) Gruff Jones (Wellington College/Scarlets), Josh Williams (Monmouth/Dragons/Exiles)
Manager: Terry Cobner
Head Coach: Rowland Phillips