Wales Under-20 coach Byron Hayward saw his side take the spoils against his former coach Mike Ruddock's Irish youngsters in Athlone.
The visitors played into a strong wind in the first half and Ethan Davies' penalty gave them a 3-0 half time lead.
Wales' pack dominated and laid the platform as they mastered the conditions after the break.
Davies' three penalties and conversion of a superb Steffan Hughes try ensured victory.
Ruddock coach Hayward as a Wales A fly-half and the latter says he "looked up" to the man who went on to coach Wales to the 2005 Grand Slam when growing up in the same village in which they lived.
But Hayward won the battle of Blaina on this occasion.
Wales U20 fly-half Davies saw one of his kicks go through the uprights after appearing to be heading for a corner flag before the wind executed a dramatic change of direction on its trajectory.
The crucial moment came after 63 minutes when Hughes benefited from a powerful Wales scrum that gave them the impetus to break the Irish youngsters' otherwise solid defence.
However, Wales also ended on top statistically in that department, executing 131 tackles to Ireland's 56 as they secured only a second win on Irish soil.
Ireland Under-20: David Busby; Cian Kelleher, Garry Ringrose, Peter Robb, Ian Fitzpatrick; Ross Byrne, Nick McCarthy; Peter Dooley, Max Abbott, Rory Burke, Sean O'Brien, Ross Molony, Peadar Timmins, Jack O'Donoghue, Dan Leavy (capt).
Replacements: Sean McNulty, Denis Coulson, Oisin Heffernan, Joe Joyce, Frankie Taggart, Jack Cullen, Conor McKeon, Dan Goggin.
Wales Under 20: Afon Bagshaw (RGC); Ashton Hewitt (Dragons), Steffan Hughes (capt, Scarlets), Garyn Smith (Blues), Joshua Adams (Scarlets); Ethan Davies (Dragons), Tom Williams (Blues); Nicky Smith (Ospreys),Ethan Lewis (Blues), Nicky Thomas (Ospreys), Scott Andrews (Dragons), James Sheekey (Blues), Will Boyde (Carmarthen), James Benjamin (Dragons) Ben Roach (Blues)
Replacements: Scott Otten (Ospreys), Luke Garrett (Dragons), Callum Lewis (Blues), Rory Thornton (Ospreys) Ollie Griffiths (Dragons), Connor Lloyd (Scarlets), Luke Price (Ospreys), Tyler Morgan (Dragons)