Rob Kearney scored the only try of a typically pulsating interprovincial derby, but man-of-the-match Heaslip was the player the table toppers turned to time and again.

The Ireland and Lions number 8 was in scintillating form in defence and attack, his best moment being a searing 60-metre break that almost saw him outpace Keith Earls.

Collectively, Leinster were at a different level as the second half wore on, scoring 13 telling points in a fifteen-minute spell coming up to the hour mark.

Jonathan Sexton, back from a fractured jaw, converted Kearney's try and kicked three penalties in all as Michael Cheika's men set up a Dublin decider against the Ospreys.

Stand-in captain Ronan O'Gara picked off a penalty and a drop goal for a valiant Munster side that kept fighting right until the end, but they were continually frustrated by Leinster's superior defence.

Regular captains Leo Cullen (shoulder) and Paul O'Connell (groin) were the most notable absentees as these great Irish rivals collided for the fourth time in a little over a year.

Leinster had a changeable wind behind them in the opening half and after Munster had briefly pressed, Sexton missed his first shot in anger since his injury against Toulouse.

Keith Earls, also back from a groin strain, made the first real thrust, invited through a gap by a flat pass from his centre partner Jean de Villiers.

Munster probed at close quarters and through O'Gara's right boot, but their lineout let them down and Leinster's defence was a constant strength.

It needed to be after a rush of blood to the head saw Shane Horgan tackle an airborne Niall Ronan as he gathered a high ball, resulting in a yellow card for the Leinster winger.

But the hosts managed to move ahead while down to 14 men, with Eoin Reddan and Brian O'Driscoll sniping through and Sexton punished a Tomas O'Leary offside for an 18th minute lead.

O'Gara put width on the ball as Munster tried to use their numerical advantage, but with Nick Williams losing his footing on the left wing, Cian Healy was able to pinch possession and Reddan cleared.

Paul Warwick had a drop goal hit the crossbar, before Munster got off the mark in the 29th minute. A solid tackle by Earls on O'Driscoll pressed Leinster into a hurried clearance and a subsequent offside allowed O'Gara kick his side level.

Leinster had the better of the exchanges, coming up to half-time, and looked the more likely to score.

Kearney collected a high ball and danced his way past four players to provide some inspiration, while Stan Wright and Isa Nacewa made good yardage through the middle and out wide respectively.

But Munster continued to cause problems of their own and Williams blew a decent opportunity when knocking on after Reddan and Kearney had collided when chasing back towards their 22.

With the sides tied at 3-3, the second half saw the pace ratcheted up. Within ten seconds of the resumption, O'Gara had used a quick feed from Niall Ronan to knock over a sumptuous drop goal for an all too brief advantage.

Led by the barnstorming Heaslip, Leinster dominated the third quarter and an ominously slick back-line move led to Kearney making the breakthrough in the 44th minute.

Gordon D'Arcy popped the ball to Sexton on a clever wraparound, the out-half then sped through a gap and drew the covering Warwick before sending Kearney over in the right corner.

Sexton added a terrific conversion for a 10-6 scoreline. The margin grew to seven points when Marcus Horan had a penalty reversed against him for punching and Sexton landed the resulting kick.

Lifeimi Mafi offered Munster some hope with a series of lively runs, but Leinster, despite a lack of sustained possession, were tightening their grip on the game. Heaslip's thundering run off a lineout showed just that.

After an O'Gara penalty miss, his half-back partner O'Leary was fortunate to avoid a yellow card. He was cautioned for a high tackle on Healy which prevented a certain 56th minute try for the Leinster prop.

Had Leinster got over the line, it would have been game over. Sexton split the posts with the resulting penalty and his more experienced counterpart O'Gara missed from halfway as Tony McGahan's charges became increasingly desperate for points.

de Villiers went off injured in his final game for Munster, but there was little the big Springbok could do to stop Leinster from marching to their 16th successive league win at the RDS.

Munster had most of the attacking play in the closing quarter, only for Leinster's tireless defence and dominant scrum to keep them at bay and O'Gara to miss a second penalty.

Mafi again looked dangerous with ball in hand, and replacement Peter Stringer added some pace to the visitors' late forays.

But there was no sign of Leinster wilting and a late surge from O'Driscoll and D'Arcy showed the potency they possess.

Having guided Leinster to their fourth victory on the trot over Munster - something they had not achieved before in the professional era - Cheika could be set for a title-winning send-off before he heads to Stade Francais next season.

Speaking after the game, a clearly satisfied Heaslip said: "It was another hard-fought battle and we're delighted to get the win and we're in contention for a bit of silverware, so we're happy.

"For the past couple of seasons we have worked very hard on our defence with Kurt (McQuilkin) and we again showed that today. Not many teams come through us, but credit to Munster because they came at us right until the end.

"They're a top quality side and we're lucky that it's us who have come out on top. The lads really dug deep and we're looking forward to facing the Ospreys in what should be a great game. They're a fantastic side right across the park."