They were kicking and screaming as they left. Underdogs on the road against their near neighbours, and reigning champions, the northern province brought their A-game to Dublin and it made for a Heineken Champions Cup quarter-final that crackled and fizzed throughout.

The intensity was unremitting.

Leinster's Dan Leavy left on a stretcher just minutes after making his second-half entrance, Ross Byrne limped off after kicking what proved to be the winning penalty and Jamison Gibson-Park departed for a HIA. That was just on the home side.

Ulster will rue the loss of captain Rory Best in the first quarter while the influential No.8 Marcel Coetzee, who all the world and its mother knew to be less than fully fit this week, managed just 52 minutes before being called to the bench.

Ulster will have more regrets besides.

Jacob Stockdale left a try behind him when dropping the ball moments before touching down in the in-goal area and John Cooney missed a sitter of a conversion that could have given them a late lead. So, so close. And so, so frustrating.

For Leinster, it is a win that leaves them just 160 minutes away from a record fifth European title and they will be glad of that after a game which they approached without the likes of Jonathan Sexton, Robbie Henshaw, Devin Toner and Josh van der Flier.

Better will be required if they are to create more history, though.

Ulster have wilted in Dublin time and again against Leinster in recent times but they gave early notice of their intention to do things differently here, claiming the lead just six minutes in through a Kieran Treadwell try.

Lightning fast off the defensive line throughout the first-half, the visitors struck gold when Garry Ringrose crabbed his way along the park just in front of the Leinster try line in search of an opening before launching a kick that was blocked down by Best.

Treadwell was the lucky recipient.

Cooney's conversion made it 7-0 for an Ulster side that had done pretty much everything well up to that point and one that had already come within a whisker of an opening try when Stockdale was set free off a scrum move only to be bundled over the sideline a few metres out.

The fact that it was four Leinster sentries who escorted him off the premises was proof that Ulster did not hold a hegemony on commitment and effort and the favourites responded with a try of their own just five minutes after falling behind.

The score was Leinster at their very best, combining the hammer and the scythe through 26 phases with Ulster's defence pulled and prodded from one side of the field to the other before Ross Byrne saw the gap from a few metres out to duck over.

A missed conversion by the out-half, followed soon after by a spurned penalty, kept Ulster's necks in front, although Dan McFarland's side suffered a grievous blow before the first quarter was out with the loss of Best to what looked like an injury to his right ankle.

The Ireland captain had started brilliantly, that block down for the try following on from a sensational turnover from Leinster's first attack, and he looked understandably distraught on the bench as Rob Herring took his place.

If Leinster were beginning to bend the game to their will – with the lion's share of territory and possession and Ulster starting to concede penalties – then it was proving less profitable than they might have hoped.

Byrne and Cooney shared four penalties in the second quarter to leave the 1999 champions 13-11 to the good at the interval and that they weren't further ahead five minutes after the restart was down to a staggering bit of, well, carelessness.

Stockdale had done everything right. Superb in the air all evening up until this point, he left Adam Byrne in his wake down the left touchline, torched Jordan Larmour and was over the try line when he dropped the ball within a hair's breath of the turf.

The TMO and referee, after some deliberation, confirmed as much.

No try, no kick for the extra two points, and Leinster made good their escape by winning a penalty at the subsequent scrum. On such tiny details can big games be decided and the import of that moment was made apparent less than ten minutes later when Leinster struck at the far end.

Jack Conan was the instigator, the No.8 breaking through from a ruck and continuing his rampage into Ulster territory despite having his pants half pulled down by a despairing tackle and feeding the supporting Adam Byrne with an offload before being felled.

The Ireland winger arrived on an angle and at a speed that ensured he was never going to be caught by a back-pedalling defense and Ross Byrne's conversion gave Leinster a five-point lead that lasted the grand sum of 10 minutes.

Luke Marshall claimed the responding try and, while it came on the back of some brilliant attacking play, it owed some to a massive slice of luck with the referee failing to punish a forward pass in the build-up and Marshall just barely getting over when Michael Lowry was free to his right.

Nonetheless, it left Cooney with a simple kick to make it 20-18 to the visitors but the scrum-half skewed his conversion wide. Another let-off for Leinster and, just as they did after Stockdale's slip, they made their opponents pay, this time with the definitive Ross Byrne penalty.

Leinster: J Larmour; A Byrne, G Ringrose, R O'Loughlin, D Kearney; R Byrne, L McGrath; C Healy, S Cronin, T Furlong; S Fardy, J Ryan; R Ruddock, S O'Brien, J Conan.

Replacements: N Reid for O'Loughlin (HT); D Leavy for O'Brien (52); J Tracy for Cronin, E Byrne for Healy and J Gibson-Park for L McGrath (all 58); M Kearney for Leavy (63); L McGrath for Gibson-Park (HIA, 66); A Porter for Furlong (67); R Kearney for R Byrne (73).

Ulster: M Lowry; R Baloucoune, D Cave, S McCloskey, J Stockdale; B Burns, J Cooney; E O'Sullivan, R Best, M Moore; I Henderson, K Treadwell; N Timoney, J Murphy, M Coetzee.

Replacements: R Herring for Best (17); S Reidy for Coetzee (52); W Herbst for Moore (56); L Marshall for Cave (63); A Warwick for O'Sullivan (72).

Referee: R Poite (Fra).