A crowd of over 48,000 watched Sexton finish with an unblemished kicking record which proved crucial as Munster fashioned a late penalty try on Friday night.
Ireland out-halves Sexton and Ronan O'Gara exchanged a succession of penalties during a defence-dominated first half at the Aviva Stadium, with the former pushing Leinster into a 15-9 interval lead.
Despite the best efforts of O'Gara and a durable Munster pack, Sexton and drop-goal scorer Rob Kearney kept Joe Schmidt's men in control of the scoreboard all the way to the final whistle.
Munster suffered an early setback when Keith Earls fielded Sexton's kick-off and injured his left leg as he set up a ruck near his 22.
Danny Barnes was brought off the bench in his place and the visitors soon took the lead, O'Gara drilling over a penalty after Donncha O'Callaghan poached a Leinster lineout.
The home side were back level by the 10th minute, their forwards gaining good ground before Sexton fired over his first of his 21 points.
Every mistake was magnified in a typically frenetic and abrasive opening, with Sexton moving Leinster 6-3 ahead after Donnacha Ryan infringed at a midfield ruck.
World Cup team-mates Sean O'Brien and Conor Murray clashed off the ball before O'Gara and Sexton exchanged penalties once again, with neither attack able to prise open a gap.
The first break eventually came when Cian Healy thundered through a couple of tackles and brought play up close to the Munster tryline. However, Leinster botched an overlap on the left and had to settle for another penalty goal from Sexton.
Five minutes later, Munster drew a penalty from a well-orchestrated maul and O'Gara had little difficulty in splitting the posts from the left.
But when BJ Botha infringed at a scrum just inside the visitors' 22, Sexton restored Leinster's six-point advantage for half-time.
The nip-and-tuck pattern continued into the second half with O'Gara and Sexton swapping penalties, although an injection of pace from Luke Fitzgerald and Fergus McFadden got Leinster's attack firing.
Isa Nacewa was crowded out in the right corner but space was beginning to open up as evidenced by midfield bursts from Barnes and Gordon D'Arcy.
Leinster moved nine points in front when, with a penalty advantage, Kearney was teed up for a sweetly-struck drop goal from 35 metres out.
Schmidt's charges were beginning to find holes and when Denis Leamy killed quick ruck ball for Leinster and received a yellow card, Sexton made it a double scores lead at 24-12.
O'Gara suffered his first miss two minutes later, yet the 14 men of Munster soon had the European champions under huge pressure.
Paul O'Connell was central to a series of lineout mauls which could and perhaps should have led to the game's first try. Leinster leaked penalties and had Jamie Heaslip sin-binned as he infringed when trying to halt the Munster drive.
It was all hands to the pump for the men in blue who managed to keep Munster out until three minutes from the end.
The visitors' scrum found the strength to shunt Leinster back towards their line and on the second such occasion, after James Coughlan almost got over, referee Pascal Gauzere awarded a penalty try.
O'Gara quickly converted but a losing bonus point was Munster's only reward after a bruising contest with their fiercest rivals.
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