Harlequins clinched victory on French soil, pulling off a superb comeback to defeat the Top 14 leaders Racing 92 in Paris on Sunday. Nolann Le Garrec put Racing ahead with a converted try but Marcus Smith responded in kind and then converted again almost immediately after André Esterhuizen crossed.
Smith added three further points with a drop goal from near halfway but the hosts reduced the deficit to 17-14 at half-time through a try from Antoine Gibert.
Racing were straight over again at the start of the second half, Le Garrec scoring his second try, and they opened up a 28-17 lead when Ibrahim Diallo crossed.
But Quins did not give up and tries from Alex Dombrandt and Jack Walker, both converted by Smith, gave them a 31-28 victory despite a late yellow card for Dino Lamb.
Leinster took revenge on La Rochelle in a repeat of last year’s Champions Cup final.
The sides have met in the past two finals, with the French team coming out on top both times, but Leinster headed home to Ireland with four points after a hard-fought 16-9 victory in their Pool Four opener.
Ronan O’Gara, the La Rochelle director of rugby, had to watch from the stands after being given a one-week touchline ban, and he saw his side take an early lead in soggy conditions through Antoine Hastoy’s penalty.
It was Leinster who found the crucial try, though, after Jonathan Danty and Joe McCarthy had been sent to the sin-bin, with Jimmy O’Brien setting up Jordan Larmour.
Levani Botia had a try ruled out after he was deemed to have crawled over the line and La Rochelle’s efforts to recover the deficit in the second half ultimately proved unsuccessful, with a brilliant long-range penalty from Ciarán Frawley calming Leinster nerves.