Coaches Andy Wood and Simon Broughton made three changes to the side which squeezed past Munster bringing in wing Adam La Grue, tight-head Conan Dunne and number eight Dan O’Donovan.
The feeling out process produced a penalty for Leinster. They went through their phases and Ulster lost their patience at a ruck for centre David Ryan to kick three in the third minute.
The concession of two quick penalties was all the invitation Ulster needed to come forward.
They were relentless in their driving game, the ball finally moved right for wing Mark Thompson to dive in at the corner for 5-3 in the seventh minute.
Strong pressure from loose forwards Scott Penny and Dan O’Donovan resulted in a knock-on for an attacking scrum which was well defended by Ulster.
The visitors blew the chance to extend their lead when fine counter-rucking was undone by a player speaking out of turn to the referee.
The remarkable capacity of out-half David Hawkshaw to withstand a hit and keep going created a penalty when full-back Michael O’Neill didn’t release after the tackle for Ryan to edge Leinster back in front.
Second row Adam Melia’s failure to hold the restart was compounded by Ryan Baird instinctively playing the ball from in front, only for out-half Bruce Houston’s kick to slide right of the posts.
A cracking tackle from loose-head Niall McEniff was matched by the burst of Ulster captain Clayton Milligan.
The visitors were growing into the game, illustrated by the short passing of their forwards, like prop Paul McGookin.
They came calling with intent and forced a five-metre lineout which flanker Matthew Crowther could not gather.
The Ulster centres David Lyttle and Stewart Moore were proving a real handful, the latter spinning a miracle ball for left wing Jonny Hunter to require Adam La Grue to be sharp in defence.
When Leinster did react, Penny could not quite break free of the clutches of fly-half Houston.
It took a stupendous piece of work on the floor by Liam Turner to garner a penalty, Hawkshaw finding touch inside the 22.
There was a fine take from Ryan Baird at the lineout, a controlled maul, significant drive from O’Donovan and sure hands across the line for Ruairi Shields to fly to the left corner.
Ryan’s conversion from the left touchline was a thing of beauty on the half hour.
The response was swift, Ulster moving well enough to force a penalty which Houston nailed for 13-8 right on half-time.
It was all to play for and Baird’s thundering carry took Leinster out of trouble.
The intervention of Reuben Pim and soft hands of Melia put scrum-half Cormac Foley through a hole to step the last man, Ryan’s conversion making it 20-8 in the 38th minute.
The game was put beyond recall when Leinster mesmerised with their movement and passing from Foley, Ryan, Turner and La Grue for prop Niall McEniff to seal the deal.
Ryan’s conversion made it 27-8 in the 45th minute.
They had solved the puzzle by moving the ball wide instead of into the guts of the Ulster midfield, their next foray drawing another three for Ryan before the centre got on the end of another sweeping move for the fourth try for 35-8 in the 48th minute.
The impact of prop Michael Milne was immediate, combining with McEniff for ground gained and rifling through the middle for the fifth try converted by Ryan.
It wasn’t long before Ryan’s inside ball had Penny strolling over without a care in the world for another seven points.
Ulster did manage their second try from Stewart Moore’s interception only for replacement Declan Adamson to send wing Shields in for his second in the 63rd minute.
Finally, Melia was there to pick up the pieces when the other Baird came up short of the line to complete the eight try haul.
At Donnybrook – LEINSTER 59 (D Ryan try, 3 pens, 5 cons; R Shields 2 tries; A Melia, S Penny, C Foley, N McEniff, M Milne try each;); ULSTER 15 (S Moore, M Thompson try each; B Houston pen, con).
15. Robert Russell (St Michael’s)
14. Adam La Grue (Terenure)
13. Liam Turner (Blackrock) / Brian O’Donnell (Gonzaga) 46 mins
12. David Ryan (St Michael’s)
11. Ruairi Shields (St Mary’s)
10. David Hawkshaw (Belvedere, Capt) / Conor Kelly (Cistercian, Roscrea) 52 mins
9. Cormac Foley (St Gerard’s) / Garrett Fitzgerald (Tullow RFC) 56 mins
1. Niall McEniff (St Mary’s) / Aziz Naser (St Fintan’s HS) 57 mins
2. Richard Bergin (St Mary’s) / Declan Adamson (St Fintan’s HS) 26 mins – temp & 54 mins
3. Conan Dunne (Kilkenny RFC) / Michael Milne (Cistercian, Roscrea) 41 mins
4. Adam Melia (Terenure)
5. Ryan Baird (St Michael’s)
6. Reuben Pim (Kilkenny) / Ronan Watters (St Mary’s) 41 mins
7. Scott Penny (St Michael’s)
8. Dan O’Donovan (St Michael’s) / Ruadhan Byron (Belvedere) 46 mins.
15. Michael O’Neill (Rainey RFC)
14. Mark Thompson (Ballymena Academy)
13. Stewart Moore (Ballymena Academy)
12. David Lyttle (RBAI)
11. Jonny Hunter (Wallace High)
10. Bruce Houston (Ballymena Academy)
9. Callum Harkin (Malone RFC)
1. Jack Walters (Exiles)
2. Clayton Milligan (Down High, Capt)
3. Paul McGookin (Ballyclare RFC)
4. JJ McKee (Antrim Grammar)
5. Josh Young (Ballyclare High)
6. Oisin Jordan (Ballymena Academy)
7. Matthew Crowther (Campbell College)
8. Jamie Macartney (Campbell College)
Replacements: Oisin Kiernan (Campbell College) for Young 30 mins; Evin Crummie (City of Armagh RFC) for O’Neill 41 mins; Niall Armstrong (RBAI) for Harkin 49 mins; Zach Kerr (Bangor GS) for Lyttle 50 mins; Jack McIntosh (Rainey RFC) for Walters 57 mins; Ben Heath (Dromore HS) for Jordan, Neil Saulters (RBAI) for Milligan both 61 mins; Ben Savage (Ballymena Academy ) for McGookin 66 mins.
Referee: R O’Sullivan, IRFU