Leinster were made to work very hard to grind out a 9-6 victory over Heineken Cup newcomers Exeter Chiefs in Dublin on Saturday.
Three Jonathan Sexton penalties proved enough to secure the result as the defending champions struggled to tame their visitors.
It could have been worse for Leinster but Argentina international Ignacio Mieres missed a last-minute penalty that would have snatched a draw for Exeter.
Led by man-of-the-match Tom Hayes, the Chiefs played the better rugby for much of a tryless Pool Five opener and looked right at home in Europe's top tournament.
Sexton twice put the home side in front with the boot in a cagey and low-scoring affair at the RDS Arena, once after 10 minutes of the first half and then again midway through the second half.
But Exeter were dogged throughout and never allowed the reigning European champions to get away from them, with Gareth Steenson matching his opposite number kick for kick.
The 28-year-old fly-half kicked penalties in the final minute of the first half and within just a couple of minutes of the Ireland number 10's second successful attempt to keep the home fans on the edge of their seat and fearing a shock upset.
The Chiefs were making it an uncomfortable afternoon for Leinster and a measure of the hosts' desperation was on show as full-back Ian Madigan decided to take on a drop goal from the halfway line.
Sexton did step up to restore order with his third penalty of the day in the final 10 minutes and the Irishmen looked to have done enough to scrape a narrow win to start the defence of their Heineken Cup crown.
Leinster did hold on and they did get off to a winning start but Exeter came within a whisker of coming away from Dublin with a draw that few would have argued that they deserved.
The tireless work of the Chiefs' pack was rewarded with a penalty just inside the Leinster half as the clock ticked over 80 minutes but, with Steenson off the field, Mieres was unable to convert it and the competition holders breathed an almighty collective sigh of relief.
Pens: Sexton 3
Pens: Steenson 2
Leinster: 15 Ian Madigan, 14 Andrew Conway, 13 Brian O'Driscoll, 12 Fergus McFadden, 11 Isa Nacewa, 10 Jonathan Sexton, 9 Eoin Reddan, 8 Jamie Heaslip, 7 Shane Jennings, 6 Kevin McLaughlin, 5 Damian Browne, 4 Leo Cullen (capt), 3 Mike Ross, 2 Richardt Strauss, 1 Cian Healy.
Replacements: 16 Sean Cronin, 17 Heinke van der Merwe, 18 Jamie Hagan, 19 Devin Toner, 20 Leo Auva'a, 21 Jordi Murphy, 22 Isaac Boss, 23 Fionn Carr.
Exeter: 15 Luke Arscott, 14 Ian Whitten, 13 Phil Dollman, 12 Jason Shoemark, 11 Matt Jess, 10 Gareth Steenson, 9 Haydn Thomas, 8 Richard Baxter, 7 James Scaysbrook, 6 Tom Johnson, 5 James Hanks, 4 Tom Hayes, 3 Carl Rimmer, 2 Simon Alcott, 1 Brett Sturgess.
Replacements: 16 Chris Whitehead, 17 Chris Budgen, 18 Ben Moon, 19 Ally Muldowney, 20 Dean Mumm, 21 Will Chudley, 22 Ignacio Mieres, 23 Sireli Naqelevuki.
Referee: Pascal Gauzere (France)
Assistant referees: Jean-Luc Rebollal (France), Cyril Lafon (France)
Television match official: Daniel Irazoqui (France)
Timekeeper: Andrew Baird (Ireland)
Assessor: Clayton Thomas (Wales)
Citing commissioner: Ray Wilton (Wales)