A strong start ultimately proved more than half the battle as early goals from Ciaran Ryan and Liam Hickey afforded Kilkenny a cushion that they were very grateful for late on.
But Brian Ryan’s Cats will move forward to the July 8 Bord Gais Energy Leinster U21HC final with big questions to answer.
For the second game running they were left hanging on at the death with a 62nd minute Jack Kavanagh Carlow goal leaving just two points in it.
Kilkenny were similarly fortunate to overcome Dublin in the quarter-finals three weeks earlier.
To their credit, they never trailed in this encounter and started brightly even if they weren’t able to sustain it.
Ryan had a goal attempt blocked after just 20 seconds and made no mistake in the fifth minute when he raised the game’s first green flag.
Hickey did the damage, spinning away from Sean Whelan before laying off to Ryan who blasted to the net.
The game took on an ominous feel in the 13th minute when Hickey netted himself after the move of the game.
Midfielder Diarmaid Byrne played the final pass after a snaking move upfield and Hickey shot right to left across goals to the top corner. That strike put the Cats 2-4 to 0-3 up and the chances of an upset already looked slim.
Carlow, however, made a spirited revival and in Chris Nolan and Ted Joyce they had a forward duo who scored a brace of points each. Free-taker Kevin McDonald totted 0-4 in the half.
But the scores simply came easier for Kilkenny who were good value for their 2-9 to 0-8 interval lead.
Hickey pointed shortly after the restart and with a double scores eight-point lead, Kilkenny looked all set to do what they do best, win big. They were left hanging on though as Peter Shaw led the Carlow fight back with an impressive 1-1 in the space of just 90 seconds.
A three-in-a-row of Carlow wides cost them though they still managed to reduce their arrears to just three points with 10 minutes remaining, 2-12 to 1-12.
Points from 2014 All-Ireland minor finalist Liam Blanchfield steadied Kilkenny again and they needed them as Kavanagh netted with time virtually up to push the Cats all the way.
C Ryan (1-2), C Martin (0-5, four frees), L Hickey (1-1), L Blanchfield (0-2), J Cleere, P Deegan, M Mansfield and J Maher (0-1 each).
Peter Shaw (1-1), Kevin McDonald (0-4, three frees), Jack Kavanagh (1-0), Chris Nolan (0-3), Ted Joyce and Marty Kavanagh (one free) 0-2.
D Brennan; C Delaney, C Wallace, E Cody; J Cleere, E Morrissey, B Troy; P Deegan, M Mansfield; C Martin, W Brennan, J Maher; L Hickey, C Ryan, L Blanchfield.
Kevin Blanchfield for Deegan (38), Luke Scanlon for Mansfield (49), Tom Phelan for Scanlon (66), Sean Morrissey for Ryan (61).
J Barron; S Whelan, G Coady, M Malone; J Murphy, D Wall, M Grady; D Byrne, C Fenlon; M Kavanagh, K McDonald, T Joyce; J Doyle, P Shaw, C Nolan.
Jack Kavanagh for Fenlon (h/t), Eoghan O’Hara for Doyle (40), Doyle for McDonald (62).
J Heffernan (Wexford).