Cronin's try decisive as Leinster hold on
Leinster 8 Ulster 3
Domestic supremacy, briefly, for one half of this pair of European strugglers but there was less evidence on hand of potential December resurgence, rather a confirmation of why both these teams have found it hard to compete at the highest level.
Ultimately, Leinster edged the contest by taking one of their several gilt-edged scoring chances; Ulster created virtually nothing in the red zone and their bonus point reflected perspiration rather than inspiration.
Leo Cullen's men were left smiling afterwards thanks to Sean Cronin's decisive 38th-minute try before a scoreless second half, which pushed Leinster to second in the Pro12 standings.
"It was a really tough game, we know each other well and we were hurting after losing in Belfast last year. I wouldn't say it was great for the spectators," said Luke Fitzgerald.
"We're pleased to get a win after two disappointing days in Europe. We showed endeavour and created some good opportunities early on," said coach Leo Cullen.
If Leinster needed an early surge of adrenalin, a surge of power through the game's opening scrum offered the perfect fillip, enabling them to swap one 22 for the other.
As they launched their early flurries, Wiehann Herbst loitered unsubtly in no-man's land and his wilful offside allowed Jonathan Sexton to fire the home side into a sixth-minute lead without really breaking sweat, if such were possible on a night when the wind chill dipped the temperature considerably.
That didn't excuse Sexton fumbling a Rhys Ruddock pass after the restart; subsequent Ulster pressure forced Leinster offside and Ulster suddenly had the chance to thieve a facile leveller. As if goaded by that thought, Paddy Jackson looked the gift horse in the mouth and promptly blinked. A bad miss.
When Jack McGrath was then guilty of not releasing, Jackson was afforded another opportunity from almost exactly the same position; he addressed his slight hook and, with 13 minutes gone, the sides were level.
After the torrential afternoon downpour, conditions were ideal and the first punt didn't arrive for a decent interval and both sides clearly wanted to play; a lovely dink from Sexton gave Fitzgerald a chance to dance down the left wing but Isa Nacewa was crowded out after receiving possession.
Ulster were assuming control until their scrum imploded to ease the home pressure. A sweeping pass off his right sent Fitzgerald clear again; Andrew Trimble was minded to run the ball into touch near the corner flag.
Leinster piled on the pressure from the ensuing lineout maul, pummelling the line until the home fans sensed a try but the TMO couldn't see the grounding of the ball.
Neither, you suspected, could Leinster.
As the forwards rumbled in vain against a stern white wall, the ball was ultimately let out to the backs.
They contrived to do no better, a shocking pass from Nacewa, who had intended to have a weekend off until hamstrung Rob Kearney was once against scratched, sending Zane Kirchner scrambling over the touchline fence.
Leinster then spurned a kickable penalty but a variety of procedural cock-ups marred the lineout; usually in this fixture it is the away side who give up these type of scoring chances.
No matter. Going to the corner again, and this time winning the aerial pill, Leinster may have had to re-form a maul after Jamie Heaslip's initial sacking but their second effort torpedoed the Ulster barricades with ease, Cronin bundling over.
They should have been out of sight from the opening second half of phased play; with Sexton deftly pulling strings hither and thither, Ruddock skipped through feeble attempted tackles from Dan Tuohy and Sean Reidy and was just held up.
From the re-load, Sexton fired out another of his rapier-like passes except it wasn't Fitzgerald on the receiving end this time, but Ben Te'o, who haplessly knocked on when all he had to was gather and slump to the ground.
Instead, he just slumped to the ground in despair. The RDS ground, filled to two-thirds of its capacity, sought to do likewise.
Still, Leinster ramped up the pressure but their recent uncertainties clouded their efforts; much as someone tries to clamber from water by seeking slippy stones en route, they were guilty of trying too hard at times.
Ulster were rarely able to exit their half but with just a score in it, they always had a chance to counter if allowed. They rarely were.
Leinster were seemingly just about good enough to preserve their advantage but not good enough to extend it; Ulster were simply not good enough to do much about anything, despite heaps of endless exertion.
The old canard about not being able to fault a team for effort usually means you can find many, many other aspects with which to apply censure.
An ankle injury to replacement Noel Reid, compounding an early departure for Luke McGrath, whose knee was unwittingly crushed by Nick Williams, interrupted an endgame that was drifting sleepily towards the inevitable.
The result, however indelicately achieved, mattered most for Leinster.
Leinster - I Nacewa; Z Kirchner, B Te'o, I Madigan, L Fitzgerald; J Sexton (N Reid 68 (G Ringrose 73)), L McGrath (E Reddan 32); J McGrath (P Dooley 60), S Cronin (J Tracy 60), T Furlong (M Moore 50), D Toner, M McCarthy (R Molony 60), R Ruddock, J van der Flier, J Heaslip capt.
Ulster - P Nelson; C Gilroy, D Cave, S McCloskey (L Ludik 73), A Trimble; P Jackson, R Pienaar (P Marshall 73); K McCall, R Best captain (R Herring 75), W Herbst (R Lutton 55), I Henderson, D Tuohy, R Diack (R Wilson 60), S Reidy (C Henry 43), N Williams.
Ref - J Lacey (IRFU)