WALES 15 IRELAND 17, Liberty Stadium, Swansea
Scorers: Wales: Tries: Ken Owens, Martyn Thomas; Con: Rhys Priestland; Pen: Priestland
Ireland: Tries: Felix Jones 2; Cons: Ian Keatley 2; Drop: Keatley
Seapoint full-back Jones, who was stepping into the shoes of neck injury victim Luke Fitzgerald, touched down in each half as he helped get new coach Eric Elwood's tenure off to a winning start.
But it was still left to Ian Keatley to nose Ireland ahead as he flung over a 70th-minute drop goal.
Wales, with the bulk of the side that won last season's U-19 Six Nations, made a strong start to the game at the Liberty Stadium and were 15-0 ahead inside the 20-minute mark.
Playing with plenty of width, Wales eked out an early penalty chance for Rhys Priestland, after an Irish ruck infringement, and the Scarlets out-half duly opened the scoring.
The Welsh, coached by Dai Rees, kicked a second penalty to the corner and Scarlets hooker Ken Owens got over for the night's first try, muscling over on a close range drive.
On 19 minutes, Ireland seemed powerless to stop full-back Martyn Thomas, another Scarlets player, from running in a second Welsh try as he took off for for the line after a quickly-taken free kick, showing great strength to cross the whitewash.
Wales did take a psychological hit though in the 27th-minute when they had a try wrongly ruled out - TV replays showed that winger Tom James had got in for a touch down but English referee Bruce Robertson, following a consulation with his touch judge, ruled it out for a foot in touch.
Crucially, Elwood's charges raised their game after that and deservedly got in for a try through Jones, who showed great power and pace to score just before the break. Keatley added the extras for a 15-7 score line.
The Irish upped the tempo again for the second half and a 55th-minute effort from Jones, which came from a flowing move started on the halfway line, allowed Keatley to convert and cut the gap to a single point.
Wales' replacement number 10 Rhys Jones then missed a penalty from distance as the hosts felt the game going from their grasp, and Ireland struck the killer blow, ten minutes from time, when Keatley landed a superb drop from 35 metres out.
The Irish pack ground out the final few minutes, showing great recycling skills and finished the game camped on the Welsh try line.
The other match in the U-20 championship, played on Friday night, finished in a 31-5 victory for England over Scotland at the Recreation Ground in Bath.
For picture highlights from the match, click here
Wales U-20s: Martyn Thomas (Llanelli/Scarlets); Alec Jenkins (Llanelli/Scarlets), James Lewis (Bedwas/Dragons), Ashley Smith (Newport/Dragons) (capt), Thomas James (Cardiff/Blues); Rhys Priestland (Llanelli/Scarlets), Robert Lewis (Neath/Ospreys); Hugh Gustafson (Llanelli/Scarlets), Ken Owens (Llanelli/Scarlets), Jamie Corsi (Newport/Dragons), Adam Brown (Bedwas/Dragons), Lou Reed (Llanelli/Scarlets), Danny Lydiate (Ebbw Vale/Dragons), James Harris (Bedwas/Dragons), Lewis Evans (Newport/Dragons).
Replacements used: Sam Kiley (Swansea/Ospreys) for Lydiate (18-22 mins), James Down (Cardiff/Blues) for Reed (53), Rhys Jones (Sale Sharks) for Priestland (58), Darren Allinson (Cardiff/Blues) for Lewis (63), Ben Flower (Bedwas/Dragons) for Owens (71). Not used: Kieron Jenkins (Glamorgan Wanderers/Blues), Richard Thomas (Aberavon/Scarlets).
Ireland U-20s: Felix Jones (Seapoint/Leinster); Shane Monahan (Dublin University/Leinster), Darren Cave (Belfast Harlequins/Ulster), Aidan Wynne (Buccaneers/Connacht), Keith Earls (Thomond/Munster); Ian Keatley (UCD/Leinster), Paul O'Donohue (UCD/Leinster); David Millard (NEC Harlequins/Exiles), Richard Sweeney (St. Mary's College/Leinster), Jamie Hagan (Greystones/Leinster), Conor McInerney (UCD/Leinster), Andrew Browne (Galwegians/Connacht), Andrew Browne (Galwegians/Connacht), Thomas Anderson (Dungannon/Ulster), David Pollock (QUB/Ulster) (capt), Sean O'Brien (UCD/Leinster).
Replacements used: Tommy O'Donnell (UL Bohemians/Munster) for O'Brien (9 mins), Ruaidhri Murphy (Lansdowne/Leinster) for Millard (half-time), Ger Slattery (Young Munster/Munster) for Sweeney (75). Not used: Neilus Keogh (UCC/Munster), David Drake (Ballymena/Ulster), Niall O'Connor (Belfast Harlequins/Ulster), Kyle Tonetti (Blackrock College/Leinster).
Referee: Bruce Robertson (England)