Another bonus point win over Pool B whipping boys Fiji next Tuesday will secure Mike Ruddock’s boys a place in the semi-finals.
The men in green made light of a creaky scrum and the concession of penalty and pushover tries and also the loss of numbers through two yellow cards (Peter Dooley and Alex Wootton).
Ireland started and finished brilliantly and held variously strong and narrow leads but the ultimate praise was for the way they turned the game back in their favour after conceding the lead (21-17) five minutes into the second-half.
Their refusal to panic was evident when they stormed back into the ascendancy with a try from star performer, centre Gerry Ringrose, whose partnership with Dan Goggin was always a threat.
Cork Constitution prop Rory Burke opened the scoring when he popped up on the blind side after a Ciarán Gaffney run.
Ringrose got his first try eight minutes later. Byrne converted both.
Winger Tyler Moore narrowed the gap for Wales with a try converted by Angus O’Brien and the out-half also converted a penalty try in response to a penalty from Byrne to leave the half time score 17-14 to Ireland.
Wales kicked on with a James Benjamin try and O’Brien the conversion to make it 21-17, but Ringrose and Byrne combined for a seven pointer before Byrne added two penalties and Cian Kelleher a fourth try to seal a memorable win.
IRELAND U-20: C Kelleher(Lansdowne/Leinster); C Gaffney (Galwegians/Connacht), G Ringrose (UCD/Leinster), D Goggin (Young Munster/Munster), A Wootton (Garryowen/Munster); R Byrne (UCD/Leinster), N McCarthy (UCD/Leinster); P Dooley (Lansdowne/Leinster), M Abbott (Cork Constitution/Munster), R Burke (Cork Constitution/Munster), D Moloney (Cork Constitution/Munster), R Molony (UCD/Leinster), P Timmins (UCD/Leinster), F Taggart (Belfast Harlequins/Ulster), J O’Donoghue (UL Bohemians/Munster, captain).
Replacements used: J Murphy (UCD/Leinster) for D Moloney (33 mins), R Foley (Cork Constitution/Munster) for McCarthy (49), D Dee (Young Munster/Munster) for Taggart (67), D Donnellan (UCD/Leinster) for Abbott, O Heffernan (Lansdowne/Leinster) for Burke (both 73), C McKeon (Lansdowne/Leinster) for Byrne, H Brewer (Terenure College/Leinster) for Goggin (both 77). Temporary. D Coulson (Lansdowne/Leinster) for Murphy (38-49).