Replacements: Joel Raikes, Lewis K Williams, Gareth Wyatt, Darran Harris, Tom Hetherington, Ed Siggery, Keiron Jenkins.
Replacements used: Tom Daly for O'Shea (56 mins), Dan Leavy for Auva'a (62), Jack O'Connell for McGrath (63), Jack Conan for Coghlan (71).
Pontypridd responded immediately, with out-half Dai Flanagan scoring a close range drop goal to bring the hosts level. They were having the better of the first quarter and the penalty count against Leinster 'A' was increasing.
A kick and chase from flanker Rhys Shellard put Andrew Boyle under pressure, resulting in a penalty for holding on. Flanagan missed the chance to put Pontypridd ahead with a difficult kick near the touchline.
Flanagan edged Pontypridd in front with a 35-metre penalty from the right two minutes later. However, the accurate boot of Reid brought Leinster 'A' level with another well-struck penalty from similar range.
Pontypridd had a golden chance to register the first try of the afternoon in the 22nd minute. They had a three-man overlap but centre Gary Williams was careless with his pass, and winger Lewis I Williams could not gather it as Leinster 'A' were given a reprieve.
Reid was kicking with real accuracy throughout, whether it was from hand or the kicking tee, helping Leinster 'A' out of trouble on several occasions.
Out-half Cathal Marsh then carved open the home defence with a fantastic dummy, only to be upended by Dafydd Lockyer.
Pontypridd responded with an attack of their own but flanker Shellard knocked the ball forward and Leinster 'A' comfortably cleared the danger.
Flanagan then converted a penalty from 20 metres to put the hosts back ahead after 33 minutes, however he missed two further scoring chances.
Firstly, after an infringement in the lineout, he missed a penalty to the right of the posts.
From the resulting play, Leinster 'A' regained possession just outside their own 22 and were penalised for crossing. Flanagan missed a straight forward kick in front of the posts.
The Pontypridd pressure paid off on the stroke of half-time as neat build-up play from the back-line resulted in Chris Dicomidis being held up five metres out.
A quick break to the left ended with Shellard setting up second row Locke for the first try of the game. Flanagan missed the conversion from the touchline.
Leinster 'A' needed to begin the second half strongly. They duly responded and were almost rewarded with a try.
After a flurry of phases in the Pontypridd final third, Colin McEntee's charges had a penalty advantage where Rhys Ruddock almost scored.
The fit-again back rower made it over the try-line but lost the ball forward. Referee John Meredith bought the play back and Reid converted the penalty confidently to reduce the deficit to 14-9.
A kick forward from Pontypridd full-back Geraint Walsh resulted in Marsh having to retrieve in his own 22. He was adjudged to have held onto the ball and Flanagan made no mistake with the 52nd minute penalty.
Leinster 'A' upped their intensity and had the lion's share of possession as the third quarter came to a close. They came close to closing the gap even further, but Reid hit the upright with a 59th minute effort from 30 metres out.
Leinster 'A' desperately needed to make their possession count and Marsh put in a defence-splitting pass which winger Boyle collected to dive over the whitewash in the 67th minute. Reid added the extras to make it 17-16.
Flanagan immediately put Pontypridd four points clear with another penalty after a lapse in discipline from the visitors.
In a pulsating final 10 minutes, Leinster 'A' thought they had secured the victory that their second half performance deserved.
Reid kicked to the corner and from the resulting lineout, young replacement Dan Leavy went over in the corner to spark jubilant scenes. The 80th minute try was converted by Reid.
But, in deepest injury-time, the points were cruelly snatched from the grasp of Leinster 'A'. The last action of the game resulted in Pontypridd dramatically winning the match after a 60-yard burst from winger Lewis Williams.
He was eventually tackled by Jack Conan and from the resulting ruck, the hosts recycled the ball and centre Dafydd Lockyer went over in the corner to give the home side the verdict by two points.
Referee: John Meredith (England)