Paris - Defending champions Leinster struggled past debutants Exeter in a scrappy 9-6 victory in their European Cup opener on Saturday.
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 were 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.
In the day's other Pool 5 game, Clermont came back from 13-6 down to trounce Scarlets 49-16 in France, running in six tries for a crucial bonus point.
Jonathan Davies gave the Welsh visitors a third-minute lead, but it proved to be their only try as Sitiveni Sivivatu, Lee Byrne, Damien Chouly, Julien Bonnaire and Napolini Vonowale-Nalaga all crossed for Clermont with a penalty try also awarded.
Olly Barkley turned in a masterful performance on his debut for new club Racing-Metro, overseeing a 22-17 victory over former two-time champions Munster in Pool 1.
"You don't win games like that against teams like Munster without a really good team spirit," said Barkley, who finished with 14 points in the Paris rain.
Barkley's counterpart, Ireland fly-half Ronan O'Gara, knocked over an early penalty as Munster dominated early play.
It wasn't until the quarter-hour mark, however, that the Irish province scored their first try, flanker Sean Dougall bouncing off a couple of weak tackles to crash over from short distance, O'Gara adding the extras.
Barkley, making his first appearance for Racing since joining from Bath earlier this month, pulled back three points with a long-range penalty.
Against the run of play, a fumbled O'Gara pass by Munster skipper Doug Howlett, the former All Black, saw Racing counterpart Jacque Cronje hack through.
Home scrum-half Maxime Machenaud was on hand to race through and touch down for a try Barkley converted to draw the scores level.
Barkley was successful with two more penalties either side of the break, before Munster wing Simon Zebo outpaced Mirco Bergamasco to score a memorable try.
Keatley knocked over the conversion to hand Munster a 17-16 lead, but shoddy defensive coverage of an innocuous kick by Murray deep inside Irish territory saw a penalty go Racing's way with five minutes to play.
Barkley made no mistake to hand the home side the lead once again, Bergamasco stretching that further with a late penalty after a Munster ruck infringement.
Last season's semi-finalist Edinburgh suffered a humiliating 45-0 home drubbing at the hands of Saracens.
The English club scored tries through Sam Tomkins, Owen Farrell, Chris Ashton, Alex Goode and Charlie Hodgson, the fly-half also scoring four penalties and four conversions for a personal haul of 25 points.
"My guys didn't play to our game plan. Instead of kicking the ball beyond the line of Saracens players, they insisted on running into the dragon's den - we could have been beaten by more," said Edinburgh coach Michael Bradley
In Pool 3, Connacht saw off Italian club Zebre 19-10.