Wales slumped to their first defeat of the Six Nations Under-21 championship following a 30-19 defeat at Galway.
The defending champions, who clinched the Grand Slam last year, were brought back down to earth following last week's emphatic win over Scotland.
But despite only one change to that side - with the return of World Cup hooker Huw Bennett - Wales never got going until the final 20 minutes.
Two tries from replacement scrum-half Richard Rees led the Welsh comeback but it was not enough to recover from a terrible first half that saw them trail 22-9 at the break.
Playing into a stiff wind, Wales got off to the worst possible start when promising Cardiff prop John Yapp was sin binned for punching after just four minutes.
While he was sat on the sideline Ireland crossed twice through No 8 Jamie Heaslip and then captain David Gannon as the home side made their extra man count.
Pontypridd's Lee Thomas and Gareth Steenson then exchanged penalties before Ireland went over for a third try inside the half-hour when centre John Hearty collected a poor pass on the bounce to leave the Welsh defence standing.
Another mistake in midfield allowed wing Tommy Bowe a free run along the touchline for Ireland fourth as a rout appeared on the cards.
Wales to their credit rallied with the two Rees tries on 67 and 77 minutes but the two missed conversions summed up a frustrating afternoon.
IRELAND U21s: A Finn; R Lane, J Hearty, G Telford, T Bowe; G Steenson, T O'Leary; J Wickham, D Fogarty, D Fitzpatrick (S Bennett, H-T), D Gannon (capt), S O'Connor (N McComb, 80), B O'Connor (C Geoghegan, 30-40, D O'Brien, H-T, R Shaw, 77), J Heaslip, O Hennessy.
Tries - J Heaslip, D Gannn, J Hearty, T Bowe. Cons - G Steenson (2). Pens - G Steenson (2).
WALES U21s: M Nuthall; I Evans (G Evans, 79), R Payne, L Thomas, F Brillante; S MacLeod, R Wells (R Rees, 53); J Yapp, H Bennett, C Griffiths, I Evans (J Mills, 53), L Charteris, J Merriman (D Maddocks,
5-14), R Dale, R Pugh (capt).
Tries - R Rees (2). Con - . Pens - L Thomas (3).
Referee: S Davey (England).