Stoic defence by Leinster in the dying seconds secured the Irish province a 16-14 win over bitter rivals La Rochelle in a dramatic finish to the Champions Cup Pool 2 match on Sunday.
The two sides have become accustomed to each other with La Rochelle – coached by former Ireland fly-half Ronan O'Gara – beating Leinster in back-to-back finals in 2022 and 2023.
However, Leinster have now prevailed in the last three meetings though Antoine Hastoy went heartbreakingly close to winning the game for La Rochelle.
Leinster's win assures them of a place in the last 16 while La Rochelle will have to wait.
"We knew we would have to front up coming over here and we did," Leinster captain Caelan Doris told Premier Sport.
"We have built up a bit of a rivalry with La Rochelle and there were a lot of battles out there and a lot of respect but we are absolutely delighted with that."
A late match winner against Top 14 rivals Toulouse last weekend, Hastoy almost repeated the feat only for his long range penalty with less than two minutes remaining coming back off the post.
It was not yet over as La Rochelle regained possession, Hastoy had a drop goal attempt blocked by Josh van der Flier, before a forward pass sealed the win for the four-time champions.
Leinster's narrow win is their 12th successive victory this season, and this run will give them hope they can set aside the pain of losing in the previous three Champions Cup finals.
La Rochelle will be kicking themselves as they failed to convert their early domination into points and trailed 16-6 with 20 minutes remaining.
However, a penalty from Hastoy and a superb try by Dillyn Leyds got them right back into it with 14 minutes remaining.
Victory put the stamp on a special day for Leinster scrum-half Jamison Gibson-Park and prop Tadhg Furlong, both of whom were making their 150th appearance for the province.
Leinster top the pool on 13 points, La Rochelle are on 10 with just one round of matches to go.
Earlier Toulon sealed their place in the last 16 with an impressive 33-21 win over English outfit Harlequins.
Toulon had it won at halftime as they scored four tries and led 26-0.
Baptiste Serin contributed 13 of his side's points, scoring a try and slotting over four conversions.
Toulon top Pool 4 by a point from Glasgow Warriors, who went through to the last 16 after beating Racing 92 29-19 on Friday.
"We are very happy qualifying especially after the four defeats in last season's competition," said Toulon backs coach Andrea Masi.
"We want to top the table, we are hungry for success."
Harlequins have yet to seal their place in the knockout stages. They host Glasgow next weekend but are vying with three other sides for the remaining two spots.
"It is simple, it all hinges on next weekend," said Harlequins head coach Danny Wilson.
"We know what we have to do, play like we did here in the second-half and not how we did in the first-half."