The scoreboard was set in motion early on as Leinster full back Noel Reid kicked a second minute penalty only for home outside half Dai Flanagan to respond with a speculative drop goal.
The contest was evenly balanced with both sides involved in a dogfight for possession in the middle of the park. Reid and Flanagan exchanged further penalty kicks at goal before Ponty spurned a chance to score as an overlap situation was squandered by a wayward pass.
Such opportunities were few and far between as the game remained largely at a stalemate. Flanagan added a third penalty and following a protracted period of home pressure, second row Craig Locke then charged over for a try to give his team a 14-6 advantage at the interval.
It was the Irish visitors who started the second half the stronger though and their efforts were rewarded with an early Reid penalty. Ponty were resolute in defence thoughand able to strike back courtesy of another Flanagan penalty.
There was little continuity to the play but plenty of tension and physicality to keep a large and vocal home crowd on their toes.
Following a sustained period of pressure, it was Leinster who struck again as winger Andrew Boyle sniped through for a try which Reid converted, narrowing Ponty's advantage to a single point with 66 minutes gone.
Dai Flanagan kicked another penalty but Ponty were having to soak up a significant amount of pressure. And it finally paid off as the Irish pack drove to the line for replacement Dan Leavy to claim a try which Reid converted to seize the lead.
Time was nearly up and it looked like game over for the Welsh side.
But the home team threw everything into an injury time assault, winger Lewis Williams forging a break and centre was Lockyer up in support to claim a dramatic late try.