South Africa’s Justin Melck was the surprise hero for Munster as his late try swung their Magners League derby 18-0 in their favour.
This clash between reigning champions Leinster and their bitter rivals Munster, the European Cup holders, was on a knife edge until Melck touched down in the 69th minute.
The former Western Province and Stormers back-rower, who is on a three-month contract, squeezed through a gap between Jamie Heaslip and Rob Kearney to put the visitors 11-0 ahead.
All Black legend Doug Howlett applied the coup de grace in the last minute, racing on to a deft kick through from Ronan O’Gara to score under the posts.
This was Leinster’s first league defeat at home to Irish opposition in five years and the manner of the loss will worry Michael Cheika and his management team.
Having lost twice to Leinster last season and not beaten them since that famous European success at Lansdowne Road in 2006, Munster were very keen for revenge.
Munster tried to sniff out an early score but O’Gara’s drop-goal attempt, after just 60 seconds, was wide of the mark.
The European champions’ lineout was a cause for concern and Leinster edged the set-piece battle, with Marcus Horan struggling often in the scrum.
However, Felipe Contepomi failed to turn pressure into points for the home side.
The Argentina star, who came into the game having landed 16 out of his 19 kicks so far this season, had an off-night in front of goal, missing four penalty attempts in the first 12 minutes.
Munster showed fewer nerves and full-back Keith Earls again caught the eye, under a flurry of high balls.
O’Gara kicked the visitors ahead in the 18th minute and the Ireland fly-half’s supreme line-kicking kept Leinster away from the danger zone.
Leinster made the better start to the second half and the visitors suffered a blow when Jerry Flannery went off with a shoulder injury.
But, in an attritional second period, Munster brilliantly ground their way into a winning position.
O’Gara tapped over a second penalty close to the hour mark and with replacement Alan Quinlan causing headaches at the breakdown, Leinster grew frustrated.
Munster’s sheer work-rate drove them on and when Earls burst down the left wing, the hosts defence was badly exposed.
The youngster passed inside for number eight Melck who made the line as Kearney and Heaslip were both caught out.
It was the game’s turning point and Leinster, losing at the RDS for the first time since October 2007, never recovered.
And a beautifully-weighted O’Gara kick put Howlett sliding over for his try to confirm the sweetest of wins.
