Defending champions Leinster were left clinging on for a nervy, narrow 9-6 win over Heineken Cup debutants Exeter Chiefs at the RDS.
Argentina international Ignacio Mieres missed an injury-time penalty to earn a draw for Exeter as Jonathan Sexton's nine-point haul proved to be just enough for the 2009, 2011 and 2012 winners.
Led by man-of-the-match Tom Hayes, the Chiefs played the better rugby for much of this tryless Pool 5 opener and looked right at home in Europe's top tournament. However, fly-half Gareth Steenson missed two of his four penalty attempts as his opposite number Sexton helped Leinster squeeze home.
Sexton was off target with his first shot at the posts, but converted his second after Exeter captain Hayes was caught offside.
Meanwhile, Steenson flicked a penalty effort to the left and wide before Exeter enjoyed their first productive spell as Jason Shoemark, Ian Whitten and Simon Alcott all made good ground.
Leinster were able to absorb Exeter's advances and Steenson suffered a second penalty miss, lacking the required direction on a long-range attempt seven minutes before the break.
Nevertheless, the hosts were forced back on the defensive and severely starved of possession and scoring opportunities. Rob Baxter's men managed to level the game on the stroke of half-time, Steenson splitting the posts after the Leinster front row had popped up in a scrum.
The home side improved in the third quarter and Sexton restored Leinster's narrow lead with a 54th-minute penalty, however his kicking radar was off five minutes later and Exeter soon managed to grind their way downfield.
Sireli Naqelevuki and Dean Mumm added their weight to the Aviva Premiership club's attack and a ruck offence allowed Steenson to kick them level with 15 minutes to go.
But better ball retention during a short rain shower got Leinster back within scoring range, and it did the trick as Exeter replacement Ben Moon tackled from an offside position and Sexton slotted the central penalty to make it 9-6.