The first half could not have been any more frustrating.
Despite Saints having more of both possession and territory the try line, aside from Gareth Denman's 17th-minute score, remained an impassable barrier.
That isn't to say that Saints did not have their chances. Ken Pisi fumbled the ball while stretching for the line in the last play of the half, Courtney Lawes was held up on the near side, a threatening five-metre scrum was penalised and George Pisi had a scoring pass intercepted.
Instead it was Leinster who went into the break leading 8-5. They had got on the score board early, Martin Moore finishing off a lineout maul after wing Sam Coghlan-Murray had cut a superb line off his left wing.
But after that it was all Saints. Denman emulated Moore, but like Jimmy Gopperth before him, Stephen Myler's conversion went straight over the top of the right-hand upright. So when the Kiwi made no mistake with a simple penalty at the end of the opening quarter it put Leinster back in front for a lead they would keep until the break.
The opening few minutes after the break followed in a similar fashion, Saints hammering away but not quite getting what they wanted.
However the breakthrough came when Samu Manoa rounded off a driving maul in his last play of the game, and despite Leinster looking dangerous - Gopperth looking right at home as the pivot of his new club - Myler landed a penalty to put the visitors two scores ahead.
Sam Olver followed suit after 65 and 75 minutes, and while Leinster showed glimpses, none more so than in the build-up to Dan Leavy's try a couple of minutes from time, the visitors had built up too much of a lead.
LEINSTER - Hudson; Fanning, Macken, Reid, Coughlan-Murray; Gopperth, L McGrath; J McGrath, Dundon, Moore, Roux, Denton, Ruddock, Jennings (c), Murphy
Reps - Cronin, Tracy, O'Connell, Furlong, Beirne, Marshall, Ryan, Leavy, Auva'a, Reddan, Cooney, Marsh, Daly, O'Shea, McFadden, Byrne, Kearney
SAINTS - Wilson; K Pisi, G Pisi, Burrell, North; Myler, Dickson; Corbisiero, McMillan, Denman, Lawes, Manoa, Clark, Dowson (c), Dickinson
Reps - A Waller, Haywood, Mercey, Craig, Day, Wood, Nutley, Van Velze, Glynn, Olver, Elliott, Stephenson, Diggin, Collins, Artemyev
4mins LEINSTER Try Moore 5-0
17mins SAINTS Try Denman 5-5
21mins LEINSTER Pen Gopperth 8-5
HALF-TIME LEINSTER 8 SAINTS 5
49mins SAINTS Try Manoa Con Myler 8-12
57mins SAINTS Pen Myler 8-15
65mins SAINTS Pen Olver 8-18
75mins SAINTS Pen Olver 8-21
78mins LEINSTER Try Leavy 13-21
FULL-TIME LEINSTER 13 SAINTS 21