And after the match Davies was full of praise for his squad.
"It is a fantastic result for us," he said.
"We had over 20 players at home and the boys came over here and produced a great performance against a side who were third in the Top 14.
"We are delighted, it puts us in a play-off tie which is where we want to be, but there is also a sense of 'what if'.
"We were so close to doing something special this year in the Heineken, but at least now we have a chance to do it in the Amlin."
"We did miss a few opportunities again, which has probably been the story of the Heineken Cup for us.
"But there is a huge amount of endeavour and quality coming through and to come here and beat Castres will do us a fantastic amount of good."