Jonathan Sexton scored all of Leinster points as they defeated rivals Munster 16-13 at the Aviva Stadium to move top of the PRO12 standings.
Having led at the break, the hosts hit back well from their defeat to Connacht last weekend to replace their Irish rivals at the summit.
For Munster, defeat at the Aviva Stadium is a setback to their play-off aspirations given Glasgow Warriors victory earlier in the day.
The match was won by returning Ireland fly-half Sexton's patiently-taken penalty, with the scores having been finely poised at 13-13 going into the final quarter of an hour.
In fact, Sexton was Leinster's only points scorer in the match, although a tremendous team effort was required to take his team over the line.
The victors' only try of the game came just before the break to give Leinster the lead for the first time in the match, having trailed to two Johnny Holland penalties for Munster.
Sexton had briefly levelled the score at 3-3, but it was his try which put the game in the hosts control.
However, early in the second half, Robin Copeland's return from the sin-bin sparked Munster into life, and they restored their advantage with their only try of the evening, scored by kicking expert Holland.
Almost immediately from the restart, Leinster levelled, but there was more than a touch of fortune about it as Munster's Francis Saili tried kicking from an offside position. Sexton had no problem with the kick, and it was 13-13.
For some time, it looked as though that was how it might end until Sexton was given another opportunity, which on a day of form, he never looked like missing, ensuring the important victory for Leinster.
Pen: Sexton 3
Pen: Holland 2
Leinster: 15 Zane Kirchner, 14 Isa Nacewa (c) 13 Garry Ringrose, 12 Ben Te'o, 11 Dave Kearney, 10 Johnny Sexton, 9 Eoin Reddan, 8 Jamie Heaslip, 7 Jordi Murphy, 6 Rhys Ruddock, 5 Hayden Triggs, 4 Devin Toner, 3 Tadhg Furlong, 2 Sean Cronin, 1 Jack McGrath
Replacements: 16 Richardt Strauss, 17 Cian Healy, 18 Mike Ross, 19 Ross Molony, 20 Josh van der Flier, 21 Luke McGrath, 22 Ian Madigan, 23 Fergus McFadden
Munster: 15 Simon Zebo, 14 Andrew Conway, 13 Francis Saili, 12 Rory Scannell, 11 Keith Earls, 10 Johnny Holland, 9 Conor Murray, 8 CJ Stander (c), 7 Tommy O'Donnell, 6 Dave O'Callaghan, 5 Billy Holland, 4 Donnacha Ryan, 3 Stephen Archer, 2 Niall Scannell, 1 James Cronin
Replacements: 16 Mike Sherry, 17 Dave Kilcoyne, 18 John Ryan, 19 Robin Copeland, 20 Jack O'Donoghue, 21 Tomás O'Leary, 22 Ian Keatley, 23 Darren Sweetnam
Referee: Ian Davies (WRU, 44th competition game)
Assistant Referees: David Wilkinson, Mark Patton (IRFU)
TMO: Simon McDowell (IRFU)