S Coghlan Murray 1 Try
The visitors opened the scoring with a first minute penalty kicked by Reid and 11 minutes later JJ responded with his opening kick of the evening.
Reid kicked his next two penalty chances to extend the lead to 9-3 before JJ added his second on the 35 minute mark, but once again Leinster produced the goods when they hit the Munster 22 and forced a fourth penalty chance in front of the posts before the break.
In the opening 40 Munster were unable to convert pressure into points whereas Leinster secured penalty chances each time they broke into the Munster half.
Costello addressed the intensity level at the break and Munster had to produce a much improved second half if they were hoping to advance.
From the off they applied the pressure attacking the Leinster line and moved within scoring distance with Dineen and Barry O'Mahony crashing through the Leinster defence and within reach of scoring. The home side were rewarded for their efforts with Hanrahan's third penalty and the sides were level once again when he slotted his fourth going into the final quarter.
Leinster responded with a Sam Coghlan Murray try right in the corner, and they were ahead by 5 going in to the last 10 minutes. Munster reduced the gap once again with JJ's 5th penalty and supporters were in store for a nervy finish with 2 points the difference and the clock winding down.
Munster secured the final penalty chance off a Leinster scrum infringement and the dream finish was on the cards, but it was not to be as the challenging kick for Hanrahan drifted wide and right.
Leinster A had done enough, winning 17-15, securing a place in the B&I Cup Final.
Munster A: S Scanlon; D Barnes, I Dineen, C Bohane (S Deasy 70), R O'Mahony; JJ Hanrahan, D Williams; J Cronin, S Henry Capt. (D Casey 70), A Cotter (M Horan 51); D Foley, I Nagle; N Ronan, B O'Mahony (S Dougall 51), CJ Stander. Replacements: D Casey, M Horan, B Hayes, S Dougall, M Prendergast, S Deasy, J Holland.
Leinster A: S Crosbie, A Boyle, A Byrne, N Reid, S Coghlan-Murray, C Marsh, L McGrath, J O'Connell, A Dundon, M Bent, T Denton, M Flanagan, B Marshall, C Gilsenan Capt., L Auva'a. Replacements: J Tracy, M Moore, T Beirne, D Leavy, A Griggs, T Daly, M McGrath.
Referee: Ian Tempest (RFU)