Leinster exacted revenge on holders La Rochelle with a chaotic, scrappy success in their Investec Champions Cup Pool Four opener.

Antoine Hastoy's nine points from the tee kept La Rochelle in the game.

The French side pushed for a late try but Ciaran Frawley's superb last-gasp penalty dashed their hopes.

Leinster's win ended La Rochelle's 16-game unbeaten run in the competition, which stretched back to the 2021 final.

In a repeat of the title showdown for the past two seasons, there was much anticipation as two of Europe's heavyweights faced off.

But the west coast of France was hit by torrential rain which limited any free-flowing rugby.

Hastoy kicked an early penalty for the hosts, but tempers soon flared as fears of a grudge match came to fruition.

With Leinster hammering the La Rochelle line, Will Skelton conceded a penalty and a melee was sparked when Jonathan Danty dragged Dan Sheehan to the turf by the back of his shirt and Leinster lock Joe McCarthy responded by tackling the French centre off the ball.

Referee Matthew Carley took a dim view of the situation and Danty and McCarthy were sent to the sin-bin.

Leinster were quicker to regain their composure and Larmour latched on to Jimmy O'Brien's pass out wide to cross, while Harry Byrne kicked an impressive conversion.

La Rochelle thought they had hit back midway through the half when Levani Botia crossed, but referee Carley adjudged he had crawled over the line and play was brought back.

Hastoy kicked his second penalty five minutes before the break but the Irish province responded as Frawley, with his first touch after replacing Byrne who was forced off for a head injury assessment, kicked a straightforward penalty.

Tense finale in France

La Rochelle started the second half on the front foot, sparked by Brice Dulin's neat break, and Ryan Baird managed to hold up prop Reda Wardi over the line.

The reigning champions were dominating the scrum as their pack showcased their power, and Hastoy reduced the deficit to one point with another well-taken penalty in the tricky conditions.

In a physical contest with a partisan crowd, replacement Charlie Ngatai injected fresh legs into the Leinster backs and he won a penalty which allowed Frawley to extend the buffer with 20 minutes left.

La Rochelle captain Pierre Bourgarit then won a penalty at the breakdown, but opted to kick to the corner and Leinster snatched the line-out and the chance was spurned.

Another opportunity to peg Leinster back was lost when Hastoy sliced a penalty wide, and Frawley sent a drop-kick wide at the other end.

La Rochelle turned down another simple three points to kick to the corner with five minutes to play but a handling error from the line-out was costly as Leinster cleared.

With the ball where his side wanted it and the clock in the red, Frawley settled a gripping encounter with his monster penalty.

La Rochelle: Dulin; Leyds; Seuteni, Danty; Favre; Hastoy, Kerr-Barlow; Wardi, Bourgarit (capt), Atonio; Lavault, Skelton; Budehent, Botia, Tanga.

Replacements: Idoumi, Sclavi, Colombe Reazel, Dillane, Picquette, Cancoriet, Iribaren, Reus.

Leinster: Keenan; Larmour; Ringrose (co-capt), Henshaw; O'Brien; H Byrne, Gibson-Park; Porter, Sheehan, Ala'alatoa; McCarthy, Ryan (co-capt); Baird, Connors, Doris.

Replacements: Kelleher, Healy, Clarkson, Jenkins, Van der Flier, Murphy, Frawley, Ngatai.