Paris - Racing 92 scratched out a 22-18 victory over Leicester in the opening round of European Champions Cup fixtures on Saturday, while twice former winners Leinster defeated Montpellier 24-17.
Racing, beaten finalists in 2016, handed a debut to South Africa flyhalf Pat Lambie as the Springbok replaced the injured Juan Imhoff after just six minutes at the Stade Yves du Manoir.
Luke Hamilton notched an early try for Leicester, the 2001 and 2002 champions, in the Pool 4 clash but hosts Racing stormed back with three quick tries from Leone Nakarawa, Bernard Le Roux and Teddy Thomas.
England wing Jonny May touched down before the break to trim Racing's lead to 19-15, with Maxime Machenaud and George Ford exchanging penalties in a cagey second half.
"Victory is a huge satisfaction because in this high-level competition you have a lot of pressure on your shoulders when your first match is at home," Racing coach Laurent Labit said.
Racing were camped deep in Tigers territory in the dying seconds but Virimi Vakatawa couldn't convert a late opportunity as the French club missed out on an attacking bonus point.
"It's a precious point that we weren't able to go and get in the second half because of a lack of control at some moments, and a lack of patience at others," added Labit.
Irish province Leinster ran in four tries through Joey Carbery, Josh van der Flier, Robbie Henshaw and Tom Daly to claim a bonus-point win at home to Top 14 high-flyers Montpellier in Pool 3.
Fijian Nemani Nadolo crossed the whitewash twice in defeat for Montpellier, without former All Blacks flyhalf Aaron Cruden due to injury, as they settled for a losing bonus point.
English champions Exeter beat Glasgow 24-15 at Sandy Park, ending the Scottish outfit's unbeaten start to the season after storming back from a 10-point deficit.
A Tommy Seymour try and a Finn Russell conversion and penalty handed Glasgow the initiative, but Exeter hit back with converted tries from Harry Williams and Jonny Hill to lead 14-10.
Gareth Steenson was perfect with the boot -- nailing three penalties -- to counter Lee Jones dotting down for Glasgow on 45 minutes, with Sam Simmonds adding a third try late on to seal Exeter's victory.
"We've got the four points, we've got the win in the first round, which is vital," Exeter boss Rob Baxter said.
"We didn't get out of the blocks as well as Glasgow did, but we have come through, got the win and denied them anything out of the game."
La Rochelle, the surprise regular-season table-toppers in France last campaign, earned a 34-27 bonus-point win at Harlequins in Pool 1 on their competition debut.
Kiwi hooker Hikairo Forbes' third-minute try laid the blueprint for a maiden La Rochelle triumph as Geoffrey Doumayrou bagged a pair of tries either side of Dany Priso touching down.
Bath shut out Italians Treviso 23-0 in Pool 5 with former Scarlets flyhalf Josh Lewis kicking 13 points to go along with scores from Zach Mercer and Aled Brew.
Reigning champions Saracens kick off the defence of their title on Sunday at English Premiership rivals Northampton, while last season's runners-up Clermont travel to Ospreys in a gruelling Pool 2.