Leinster escaped from France with a seriously hard-earned Investec Champions Cup victory as they held on to beat La Rochelle 16-14.
Sam Prendergast scored three penalties and converted Joe McCarthy's first-half try at Stade Marcel-Deflandre.
In a frantic finish, La Rochelle's Antoine Hastoy hit the post with a penalty that would have won the game, and then had a drop-goal blocked.
Leinster had to go to the well to withstand intense pressure at the death but they saw it out to make it three pool wins from three.
It was the sides' sixth meeting since 2021 with Leo Cullen's men having won both clashes last season, including a 16-9 win at the same venue.
While Leinster have won all matches this season, this was their biggest challenge to date and the first real test of their new and improved defensive system.
They passed with flying colours.
For all of the hosts' possession in the first half, they were restricted to two Hastoy penalties and denied on a number of occasions by tenacious Leinster tackling.
Captain Caelan Doris, Jamison Gibson-Park and Jordie Barrett all came up with big plays to keep Ronan O'Gara's men out.
Leinster, beaten finalists in the last three seasons, made 194 tackles in total, and turned the ball over ten times.
It was always likely to be nip and tuck with Prendergast's 12th-minute penalty from distance levelling things up after Hastoy knocked over an early kick.
The setpieces were messy with both sides conceding penalties and free kicks, while soon after La Rochelle stole a lineout throw, Hastoy edged them back in front when Robbie Henshaw was penalised in midfield.
A trademark run by Ryan Baird just before the half-hour mark got Leinster in position to strike for their only try of the game.
The flanker was involved in the build-up, neatly combining with Jamie Osborne on the 22 before the wing popped it to McCarthy, who had a run in. Prendergast converted to put Leinster ahead.
They could have had a bigger advantage at the break but the La Rochelle pack disrupted a maul close to the line after Hastoy had an effort ruled out for a Jack Nowell knock-on.
Cullen sent on powerhouse replacements Jack Conan, RG Snyman and Rabah Slimani in the 47th minute and they had an immediate impact with the flawless Prendergast adding two penalties to push the lead to 16-6.
But Stade refused to buckle and ensured a nervy finale with Hastoy reducing the deficit off the tee with 20 minutes left and then setting up Leyds for a brilliant try.
After a number of phases in the Leinster 22, the out-half cross-kicked for the South African winger, who had Ciarán Frawley in close attendance.
With little space to work in, Leyds dinked it ahead and dotted down to ensure a tense finish.
Replacement Ross Byrne and Barrett both missed penalties, which would have given the visitors a cushion as the clock wound down.
Hastoy tried a shot from his own half after Leinster infringed at a breakdown and after it hit the post, Leinster failed to clean up.
The out-half's drop-goal attempt from the subsequent scrum was blocked down but they retained possession for three minutes of overtime, before a forward pass brought a thrilling contest to an end.
Leinster top Pool 3 on 13 points with La Rochelle second, both sides assured of making the round of 16.
Cullen's side host Bath at Aviva Stadium next weekend.
SCORERS
La Rochelle: Try - Leyds
Pens: Hastoy (3)
Leinster: Try - McCarthy
Con: Prendergast
Pens: Prendergast (3)
La Rochelle: Brice Dulin; Jack Nowell, Ulupano Seuteni, Jules Favre, Dillyn Leyds; Antoine Hastoy, Tawera Kerr-Barlow; Reda Wardi, Quentin Lespiaucq, Uini Atonio; Thomas Lavault, Kane Douglas; Paul Boudehent, Oscar Jegou, Grégory Alldritt (captain).
Replacements: Nikoloz Sutidze (for Lespiaucq 77), Alexandre Kaddouri (Wardi 39), Georges-Henri Colombe (Atonio 33), Ultan Dillane (Lavault HIA h/t (Douglas 46), Levani Botia (Favre 56), Judicaël Cancoriet (Lavault 47), Matthias Haddad (Cancoriet 63), Hoani Bosmorin (Dulin 76).
Leinster: Jordie Barrett; Jimmy O'Brien, Garry Ringrose, Robbie Henshaw, Jamie Osborne; Sam Prendergast, Jamison Gibson-Park; Cian Healy, Rónan Kelleher, Tadhg Furlong; Joe McCarthy, James Ryan; Ryan Baird, Josh van der Flier, Caelan Doris (captain).
Replacements: Gus McCarthy (for Kelleher 73), Andrew Porter (Healy 20), Rabah Slimani (Furlong 47), RG Snyman (J McCarthy 47) , Jack Conan (Baird 47), Luke McGrath (Gibson-Park 71), Ross Byrne (Prendergast 61), Ciarán Frawley (O'Brien 61).
Referee: Nika Amashukeli [Georgia]
