La Rochelle marked their arrival in the Top 14 with a brave 22-17 victory against Castres at their home ground of Stade Marcel Deflandre.
Castres had the majority of play, but were punished by their hosts for failing to make their possession count.
Tries from Sebastien Boboul and Benjamin Ferrou put the home side into a 12-3 lead after just 16 minutes but despite constant pressure from Castres they could not close the gap before the half-time whistle.
Iosefa Tekori dragged the visitors back into the contest with a converted try, but Norman Ligiari galloped clear to score another try for La Rochelle.
Castres set up a tense finish when Chris Masoe released fly-half Cameron McIntyre to reduce the deficit to five points, but though Florian Denos came tantalisingly close to scoring La Rochelle held on for a famous win.