The Argentine scored the only try of the game on 18 minutes after Zack Henry gave visitors Pau the lead with a penalty.

Urdapilleta then added the extras to his own score, before Julien Dumora extended the home side's advantage with a penalty on 22 minutes.

Henry responded with a kick of his own three minutes later, before Urdapilleta added another three points to the home side’s score.

Henry fronted the Pau fightback as he reduced the deficit to one point with a penalty and a drop-goal in the second half, but Ben Botica’s penalty sealed victory for a Castres side who will face Harlequins and Munster Rugby in Pool B when this season’s Heineken Champions Cup gets underway in December.

Bordeaux Bègles, who will face Leicester Tigers and Scarlets in Pool B, were beaten 27-15 away at Biarritz Olympique.

Brett Herron, Lucas Peyresblanques and Romain Lonca all crossed as the home side dominated for much of the game, with Bordeaux’s only response a penalty from Matthieu Jalibert, until the closing stages.

Alban Roussel and Yoram Moefana both crossed the whitewash for Bordeaux in the final ten minutes, but last season's Heineken Champions Cup semi-finalists were soundly beaten.

Elsewhere, Enzo Hervé racked up 26 points as Brive recorded a convincing 36-15 win over USAP, whose points came entirely from the boot of Tristan Tedder.

Castres Olympique fly-half Benjamín Urdapilleta tallied 10 points as his side edged Section Paloise 16-12 in the opening round of this season's TOP 14.