Leinster will defend their Pro14 title against Munster on 27 March having secured their final berth by beating 14-man Ulster 38-19.
Early tries from Marcell Coetzee and Robert Baloucoune saw Ulster storm to a 12-3 lead inside 14 minutes.
Michael Bent, Josh van der Flier and Ed Byrne replied for Leinster while Ulster had prop Andrew Warwick sent off.
Rhys Ruddock gave the visitors the crucial bonus point before Nick Timoney and Dan Sheehan traded late scores.
The result puts Leinster 11 points ahead of Ulster in Conference A with just two games remaining.
Leo Cullen's side are seeking their fourth straight league title, and will arrive into the final as favourites to continue their total dominance of the competition.
For Ulster, whose only two defeats in this season's competition have come at the hands of Leinster, it is another reminder of the steps still to be taken if they are to join their provincial rivals in the elite tier of European rugby.
The European Challenge Cup and the inaugural Rainbow Cup, both of which will be played in April, are now the northern province's remaining avenues to silverware this season.
Unflappable Leinster turn first-half tide
Although undoubtedly a pivotal moment that played into Leinster's hands, it should be noted that Warwick's 31st minute red card was not the game's turning point.
By the time the prop was dismissed for leading with his elbow, the reigning champions had already turned the tide on Ulster, who produced the start they would have dreamed of.
With Devin Toner in the sin-bin for a high tackle, Ulster pounced early and drove towards the line with Coetzee punching the final hole in the defence to announce his return to the side.
Another returning figure was wing Baloucoune, making his first start in 13 months and instantly producing the clinical finishing that has so quickly endeared him to the province's fans.
He fought off a challenge to finish in the corner after an outstanding Stuart McCloskey offload had allowed John Andrew to feed Baloucoune.
It was the perfect opening quarter for Ulster, made better by Leinster being reduced temporarily to 13 with Jimmy O'Brien yellow carded for making contact with Ian Madigan's head in the build up to the try.
Ulster had built up enough momentum to break the spirit of perhaps any other Pro14 side but Leinster, without their array of first team stars who remain with the Ireland squad, stuck to their gameplan in the knowledge that results would come.
Their first sustained spell of pressure saw Bent eventually crash over, and just three minutes later a smart Max O'Reilly break brought the visitors to within inches of the line again, with Stuart McCloskey sent to the sin-bin for illegally disrupting the move.
From the tap-and-go penalty Van der Flier crossed, and having been up against it, Leinster were ahead.
Warwick's red card followed and to compound Ulster's misery, Coetzee was forced from the field having picked up a hamstring injury.
Leinster were playing with momentum and confidence, Ulster were scrambling and could do little as their opponents created space out wide with Byrne extending their lead before the break.
Leinster claim all-important bonus-point
With 40 minutes left to salvage their campaign, Ulster's 14-men were in need of a moment of magic to spark the game back into life.
The hosts thought they had found it in the 50th minute when a strike play on halfway saw Baloucoune slalom through to score, but the effort was chalked off after McCloskey was judged to have obstructed a tackler as the wing sliced through.
It was another demoralising blow for the hosts, and a reprieve that immediately focussed Leinster minds once more.
Seven minutes later Ruddock drove over for the fourth try, to effectively deliver the knock-out blow that ended not only Saturday's contest, but the race for top spot in Conference A.
Ruddock was himself sin-binned shortly before Timoney put another Ulster score on the board and when Cormac Izuchukwu was shown the fifth yellow of the day, replacement hooker Sheehan added the final try of the game.
Ulster: Lowry; Baloucoune, Hume, McCloskey, Stockdale; Madigan, Cooney; O'Sullivan, Andrew, O'Toole; O'Connor, Treadwell; Timoney, Murphy, Coetzee.
Replacements: McBurney, Warwick, Moore, Izuchukwu, Reidy, Mathewson, Moore, Lyttle.
Leinster: O'Reilly; Kelleher, O'Brien, O'Loughlin, Kearney; R Byrne, McGrath; E Byrne, Tracy, Bent; Toner, Fardy; Ruddock, Van der Flier, Penny.
Replacements: Sheehan, Dooley, Clarkson, Molony, Murphy, R Osborne, J Osborne, Dunne.