Fellow Ospreys academy talent Alun Wyn Jones went over in the first half to give Wales a lead they never let slip. Hook also converted both tries, proving crucial as Ireland hit back with an injury-time through Fergus Carr. And coach Chris Davey will know his team could have won by more than they did.
Ireland were reduced to 14 men as early as the third minute when David Toner was sent to the sin bin for stamping. Yet it was Ireland who led through a Conan Doyle penalty when the second-row returned ten minutes later. But that did not stop the Welsh pack from dominating their opponents for the lion's share of the first half. Carmarthen's Dominic Day was immense in the lineout while the front row had Ireland's scrum in knots.
Neath half-backs Martin Roberts and James Hook always looked threatening and it was a moment of class from the outside-half that set up Wales's opening try. Hook's one-handed pick-up rescued a Welsh attack, after Tom Riley had dropped the ball, to send Scarlets academy wing Darren Daniel motoring down the right-hand wing.
Daniel's lightning pace took Wales to within touching distance of the try line. And when Day collected Duane Goodfield's lineout, Wyn Jones rumbled over on 28 minutes. Hook converted from out wide. But for all their possession, Wales failed to make a greater impact on the scoreboard and their game collapsed before the break when Day and then prop Phil Osbourne both saw yellow cards in the space of four minutes before the break.
Doyle punished the first foul but saw his second effort strike the post to leave Wales 7-6 ahead until the final minute of the game. Rhys Shellard's neat pass sent Hook storming under the posts to finally see off Ireland in the 79th minute. Hook added the conversion and it proved vital as Carr rounded off a stunning final attack by Ireland.
Ireland U21: F Carr; P Durcan, D Cave, F McFadden (J Sexton, 74), M Williams; C Doyle, P Marshall (D Williams, 61); D Hurley, S Philpott, P Doran-Jones, D Toner, D Touhy, M Essex (B Holland, 68), S O'Brien, E Uzoigwe
Try - F Carr. Con - J Sexton. Pens - C Doyle (2)
Wales U21: J Roberts (A Thomas, 78); D Daniel, A Bishop, T Riley (D Hewitt, 65), C Czekaj; J Hook, M Roberts (L Davies, 61); R Gill (I Jones, 74), D Goodfield (E Shervington, 78), P Osbourne, A Wyn-Jones, D Day (W Jones, 71), C Everett (B Lewis, 50), T Smith (capt), R Shellard (I Jones, 42-47)
Tries - A Wyn Jones, J Hook. Cons - J Hook (2)