Danny Wilson’s men looked set to claim a narrow victory following a second-half Lewis Williams penalty to nullify Shane Layden’s try for the hosts.
But Ireland’s youngsters rallied in the final quarter with drop-goals from Paddy Jackson and Luke McGrath to snatch the triumph.
Wales were clearly suffering from early match-day nerves and made a frantic and error-strewn start to the encounter.
Ireland took advantage of Wales’ jitters and dominated the opening exchanges but were unable to turn pressure into points with Jackson missing two shots at goal.
Wales weathered the storm and Sam Davies slotted a neat drop-goal to take the lead.
But the hosts responded in perfect fashion and JJ Hanrahan burst through Wales’ midfield defence, mid-way through the half, before firing a pin-point long pass for Layden to score in the corner.
Jackson’s conversion fell narrowly short of the posts but the try had handed Ireland a 5-3 lead.
Wales could have gone into the interval trailing by even more had it not been for the heroic defence of Ross Jones and Cory Allen following another sweeping Irish move.
With the win at their backs Wales produced a far more second-half performance and Williams booted the visitors into the lead as Jackson continued to fire wide.
But the Ulster fly-half fired a drop-goal with 10-minutes to spare to re-gain the lead at 8-6 before McGrath sealed the victory.
Ireland U20
Try: Hanarahan; DGs: P Jackson, L McGrath
Wales U20
Pen: L Williams; DG: S Davies
