There is a theory that form counts for not very much when it comes to this fixture, that you can take to your bed feeling unwell for three whole weeks and then hop up brand new at the sight of the old foe coming up the garden path.
In this instance Leinster were the ones bedridden as Munster walked through the gate with neither flowers nor get well card. Weighing heavily also on Leinster minds was the distinctly odd combination of needing a win to secure a record five in a row over their opponents, and at the same time avoiding their worst start to the season in living memory. They slept easier last night with the more enviable record secure, and with Racing Metro bringing their heavyweight side to the RDS on Saturday.
To that end, they got Jonny Sexton through nearly half an hour in one piece, and he should be able to kick freely -- the quad injury he's carrying is specifically a kicker's injury. All of which was a huge relief to coach Joe Schmidt who felt better the longer the game developed.
"As the second half wore on I felt we were getting a bit more space and started to break the defensive line down with line breaks," he said. "When Eoin Reddan came on (56 minutes) we were just starting to get a little more front foot ball. Front foot and Reddan means you're going to get more pace into your game."
This first big rugby night in the Aviva was always an absorbing affair, but its quality went up significantly in that last half hour. This is far better news for Leinster who looked quick and penetrative when the game opened up a bit. Munster on the other hand were faced with needing to score a try when, on 70 minutes, Brian O'Driscoll had got the first touchdown of the game, courtesy of a lovely offload from man of the match Sean O'Brien. Whatever happened in that limited window, you never felt it was going to involve Ronan O'Gara lining up a conversion.
It would have involved a significant turnaround too, given that Munster had traded worse in the second half, despite O'Gara edging them ahead twice in the third quarter after the teams had turned over 3-3 at half time.
"We're bitterly disappointed with the result," Tony McGahan said afterwards. "I thought it was a good derby game in wet conditions and both sides went at it but I think field position cost us."
For a first big game in the Aviva is was gripping and entertaining, and while the Munster fans left downcast, it was a very good night's rugby, despite the slippy track after a day of heavy showers.
Of the newcomers to this fixture, Dominic Ryan must have enjoyed it the most. He has more rough edges than an uncut diamond, and in this contest it's often a useful condition. We weren't long into the game when Ronan O'Gara was toe-poking him after the young flanker had lined him up and delivered a colossal hit that was borderline on time. Ryan revelled in it all, well all except two penalties -- the second very harsh -- for coming in from the side at the ruck.
So too did Johne Murphy enjoy himself, albeit in a different way. The attraction of Ian Dowling, the man he has replaced on the wing, is that he combines enormous competitiveness with low error count. Murphy is doing the same but with more threat. He saved a try in the second half when cutting off Ryan from a wide pass to two free attackers.
Munster weren't helped by losing Lifeimi Mafi to the bin in the second half after a high tackle on Rob Kearney. It was mild compared to the swinging arm that could have done serious damage to Gordon D'Arcy in the first half. Even allowing for the strange workings of the Magners League disciplinary machine, it would be a surprise if the Tongan doesn't have a case to answer this week. Which would be more bad news for Munster ahead of the trip to London Irish on Saturday.
Certainly Leinster will feel a whole lot better now about the Heineken Cup campaign. They have a bit to go yet but this was an aggressive step in the right direction.
Eventually their patience was rewarded on 70 minutes when O'Brien produced a perfect offload for O'Driscoll to score down the outside after they had engineered the numbers out wide. Nacewa's conversion gave them a four point lead. They held onto it.
Scorers -- Leinster: B O'Driscoll try; I Nacewa 2 pens, con) Munster: R O'Gara 3 pens).
Leinster: R Kearney; S Horgan (J Sexton 55), B O'Driscoll, G D'Arcy, L Fitzgerald; I Nacewa, I Boss (E Reddan 56; C Healy (H van der Merwe 61), R Strauss, M Ross (S Shawe 77), N Hines, D Toner, D Ryan, J Heaslip (capt, R Ruddock 77), S O'Brien
Munster: P Warwick; D Howlett, L Mafi (yc 45-55), S Tuitupou, J Murphy; R O'Gara, T O'Leary; M Horan, D Varley, T Buckley, D O'Callaghan, D Ryan (M O'Driscoll 65), A Quinlan (D Wallace 55), D Leamy (capt), N Ronan.
Referee: J Garces (Fra).