However, under the new system, they face a play-off for the title in Athlone next week against either Leinster or the winners of the Ulster v Connacht clash.
The match, moved from vandal-damaged Thomond Park, attracted a sizeable and animated crowd that got full value for money.
Munster were the better side, but lived dangerously and were left hanging on to the necessary points advantage at the end.
After Leinster had carved out one particularly good opening, Munster took the lead. Captain Billy Holland led the way with a spectacular break and found Ian Hanley in support, the full back going in for a fine try. Conal Doyle converted, but Leinster struck back with two excellent penalties from Jonathon Sexton.
Munster got an added bonus in injury time. Doyle's long-range penalty came back off an upright, Leinster failed to clear and winger Ed Mills charged down an attempted clearance to get in for the try that Doyle converted.
Although Munster stormed into a full-frontal assault early in the second half, Leinster clawed their way back with a third penalty from Sexton.
That encouraged the visitors, and it didn't help that Munster number eight David Sherry was rather harshly sin-binned by referee Peter Ferguson.
It led to some anxious moments that called for a stern defence, which held until Sexton kicked a fourth penalty just seconds before Sherry's return.
But when Sherry came back, young Barry O'Mahony joined him as a substitute and made an immediate impact.
With the game in the balance, O'Mahony took up position at out half, blitzed his way through the Leinster defence and sent Hanley galloping away. The full back was stopped short of the line, but O'Mahony was back in support to crash over and Doyle converted from the touchline - 21-12.
But despite Munster's continuous territorial advantage, the title nearly slipped from their grasp in the closing moments.
Leinster struck with a magnificent 81st-minute try from centre Conor Donohue, with Sexton converting.
In one last desperate throw of the dice, the visitors came agonisingly close to another try and victory. The ball skidded out of the hands of substitute Kieran Moloney and Munster breathed a huge sigh of relief.
: I Hanley (UL Bohemian), E Moloney (UCC), T Gleeson (UCC), E Ryan (UCC), E Mills (Dolphin), C Doyle (Garryowen), D Williams (UCC), D Hurley (UCC), B Duggan (UCC), D Ryan (Highfield), M O'Hea (Clonakilty), C Kenefick (UCC), B Holland (UCC, captain), D Sherry (Garryowen), M Essex (UCC).
: R Noonan (UCC) For O'Hea (52), B O'Mahony (UCC) for Essex (70), C Parkes (UL Bohemian) for Duggan (76).
: F Carr (Blackrock), K Barden (Old Belvedere), F McFadden (UCD), C Donohue (Dublin University), S Hanratty (Dublin University), J Sexton (St Mary's), D Coughlan (Lansdowne), K O'Neill (Dublin University), G O'Meara (Lansdowne), P Doran Jones (Dublin University), D O'Reilly (Dublin University), D Toner (Lansdowne), L Mantle (Greystones), S O'Brien (UCD), D Laffan (Dublin University, captain).
: M D'Arcy (Dublin University) for Coughlan (46), K Moloney (Blackrock) for O'Meara, C Culleton (Dublin University) for O'Neill, C O'Sullivan (Greystones) for Barden (all 73).
: P Ferguson (Ulster).
LEINSTER went on a second-half scoring spree to clinch the U19 inter-provincial title in style at Dooradoyle last night.
Munster had a bright start and took the lead with a William Staunton penalty after three minutes, but it all went downhill from there.
Kenny Keogh kicked the equalising penalty two minutes later and then added the extra points to a try from Felix Jones.
Leinster had a second try from Shane Monaghan early in the second half and then pulled away. Keogh kicked a penalty and converted a try from Ian Keatley to make it 25-3.
With the title in the bag, Leinster flourished and added further tries from Barry O'Flanagan, Jones and Ian Condell, with Keogh kicking all three conversions.
: W Staunton (Garryowen), S O'Sullivan (Sunday's Well), D Lynch (Clonakilty), D Collins (Kilfeacle), P Thompson (Garryowen), A Coughlan (Sunday's Well), T Cahill (Bruff), R Wilmott (Bandon), N Bourke (Cork Con), R O'Neill (Sunday's Well), C McNamara (Garryowen), N Keogh (Bruff), O Keely (Corinthians), D Nathan (Cork Con), T O'Donnell (Clanwilliam, captain).
: C O'Neill (Clonakilty) for Nathan, B Rowley (Garryowen) for O'Neill, P Broghan (Midleton) for O'Sullivan, E Lane (Newcastlewest) for Collins.
: M Skelton, S Monaghan, S English, F Jones, K Keogh, I Keatley, S Cranley, J Hagan, D Gilchrist, R Sweeney, C McInerney (captain), N Cummins, B O'Flanagan, K Sheehan, I Condell.
: R Brosnan for Gilchrist, D Farrell for Cranley, S Dunlop for O'Flanagan, C Jebb for English.
: J Peake (Ulster).