Leinster were inches away from the perfect start when Charlie Molony collected a loose ball to shoot up the left where his give-and-take with James O’Dwyer almost did the trick.
It was enough to force a hasty clearance, allowing the home side to come hard again through Derry Moloney on the counter and Dylan McNeice from a lineout move.
Ulster were unable to relieve the pressure, a maul moving at speed for hooker Lee Fitzpatrick to break away and ground the ball in the seventh minute.
The visitors’ kicking game invited more trouble. Leinster were keen to exploit the stand side, Ethan Black poking the ball into space where O’Dwyer could not quite grab the opportunity at hand.
Leinster mixed their game to maximum effect when a ball out the back from O’Shaughnessy drew the Ulster defence up for the out-half to stab a grubber through for Johnny O’Sullivan to nab the second try, converted by O’Shaughnessy in the 13th minute.
Ulster made the first serious dent from a scrum penalty. Their front row was conspicuous by its presence, a number of drives culminating in prop Blake McClean crossing for Quinn Armstrong to land the conversion.
In a flash, Fitzpatrick had responded in a style similar to his first try, benefiting from Donncha McGuire’s athletic lineout take to bounce tacklers on his way to the line for 17-7 in the 26th minute.
O’Shaughnessy snatched an interception to turn defence into attack without the clinical edge to make it pay.
A yellow card for Duinn Maguire triggered an Ulster attack which produced a penalty by Armstrong for 17-10 at the break.
The high-flying Black secured possession from the kick-off and Charlie Molony was next to show up, weaving a path to glory from outside the 22 for O’Shaugnessy to kick the extras.
Armstrong scythed through a gap and came for a second touch to profit from light numbers on the fringe of a ruck for a fine try which he also converted in the 47th minute.
Again, Leinster had the tools to deal with this setback, the backline engineering positive play. Predictably, the lineout was the vehicle for flanker Dermot Collins to claim a try, converted by O’Shaughnessy.
A wayward pass was enough to cause hesitation in Leinster’s defence so that Fraser Cunningham could speed towards the sticks, Armstrong’s conversion making it a one-score game in the 54th minute.
Once again, Leinster had the answers as replacement Luke McLaughlin blasted home for O’Shaughnessy to add the two on top and the hooker made it a quickfire brace from a driving maul for Charlie Hempenstall to convert.
Scorers:
Leinster – L Fitzpatrick, L McLaughlin 2 tries each; D Collins, C Molony, J O’Sullivan try each; C O’Shaughnessy 4 cons; C Hempenstall con.
Ulster – Q Armstrong try, pen, 3 cons; B McClean, F Cunningham try each.
Teams
Ulster
15\. James Kerr (Royal Belfast Academical Institution), 14. Henry Ralston (Campbell College Belfast), 13. Fraser Cunningham (Royal Belfast Academical Institution), 12. Quinn Armstrong (Wallace High School), 11. Russell Alo Veikune (Campbell College Belfast), 10. Frank Davis (Belfast Royal Academy), 9. Callum Irvine (Ballymena Academy), 1. Blake McClean (Royal Belfast Academical Institution), 2. Connor Magee (Banbridge Academy), 3. Rio McDonagh (Wallace High School), 4. Ryan Halpin (Down High School), 5. Zack McCartney (Coleraine Grammar School), 6. Matthew Heasley (Dromore High School), 7. Thomas Dougan (Royal School Armagh, Captain), 8. Callum McKinney (Campbell College Belfast).
Replacements: 16. James Clark (Royal Belfast Academical Institution), 17. Zak Molyneaux (Royal Belfast Academical Institution), 18. Nathan Noble (Sullivan Upper School), 19. Harry Thallon (Sullivan Upper School), 20. Sam Warwick (Wallace High School), 21. Callum Soper (Royal Belfast Academical Institution), 22. Oliver Berry (Methodist College), 23. Josh Gibson (Royal Belfast Academical Institution).
Leinster:
15\. Derry Moloney (Blackrock College)<br>
14\. Johnny O’Sullivan (Blackrock College)<br>
13\. Ethan Black (St Michael’s College)<br>
12\. Charlie McConnell (St Michael’s College) / Brian O’Flaherty (Blackrock College) 64 mins<br>
11\. Charlie Molony (Blackrock College)<br>
10\. Conor O’Shaughnessy (Blackrock College) / Charlie Hempenstall (Wesley College) 58 mins<br>
9\. James O’Dwyer (Gonzaga College) / Luke Fogarty (The King’s Hospital) 58 mins<br>
1\. Ed McLaughlin (St Michael’s College) / Max Doyle (Clongowes Wood College) 52 mins<br>
2\. Lee Fitzpatrick (Cistercian College Roscrea) / Luke McLaughlin (Gonzaga College) 52 mins<br>
3\. Duinn Maguire (St Michael’s College) / Sami Bishti (Blackrock College) 44 mins<br>
4\. Dylan McNeice (Catholic University School)<br>
5\. Donncha McGuire (Blackrock College, Captain)<br>
6\. Joe Elliott (St Michael’s College) / Charlie Kennedy (Gonzaga College)58 mins<br>
7\. Dermot Collins (Clongowes Wood College)<br>
8\. Ben Blaney (Terenure College) / Sami Bishti (Blackrock College) 40 mins – temp) / Charlie Meagher (CBC Monkstown) 58 mins.
Referee – M Enderbey, IRFU.