Leinster survived a scare from Heineken Cup newcomers and held on to beat Exeter Chiefs 9-6 at the Royal Dublin Society (RDS) Stadium.
Leinster, the champions in 2009, 2011 and 2012, were forced to grind their way to victory, with Irish international fly-half Jonathan Sexton kicking three penalties.
Sexton put Leinster ahead in the 11th minute after former Ulster centre Ian Whitten was penalised for playing an opponent in the air.
But the expected avalanche of points never materialised and Exeter drew level on the stroke of half-time when Gareth Steenson succeeded with a penalty after two earlier misses.
Sexton put the champions back in front after 53 minutes but Steenson again pulled Exeter level 12 minutes later when Leinster were penalised for slowing the ball down at a ruck inside their own 22.
Exeter replacement prop Ben Moon was then punished for straying offside in the 74th minute and Sexton gobbled up the opportunity with the decisive penalty in front of the posts.
Exeter had a chance to level in the last minute but Ignacio Mieres went well wide with an optimistic 48-metre penalty attempt.
"It was no surprise to us how tough they were to break down. They are a formidable side," said Leinster coach Joe Schmidt.
"They are greater than the sum of their parts, well coached, well organised and hard to break down."
Final Score Leinster 9 (3) Exeter 6 (3)
Penalties: Sexton 3
Penalties: Steenson 2
Referee: P Gauzere (France)
Leinster: I Madigan; A Conway, B O'Driscoll, F McFadden, I Nacewa; J Sexton, E Reddan; C Healy, R Strauss, M Ross; L Cullen (capt), D Browne; K McLaughlin, S Jennings, J Heaslip.
Replacements: S Cronin, H van der Merwe, J Hagan, D Toner, L Auva'a, J Murphy, I Boss, F Carr.
Exeter: L Arscott; I Whitten, P Dollman, J Shoemark, M Jess; G Steenson, H Thomas; B Sturgess, S Alcott, C Rimmer; T Hayes, J Hanks; T Johnson, J Scaysbrook, R Baxter.
Replacements: C Whitehead, C Budgen, B Moon, A Muldowney, D Mumm, W Chudley, I Mieres, S Naqlevuki.