Wales fly-half Rhys Priestland kicked 20 points as Bath ground out a battling 25-22 win over Pool 4 rivals Pau at the Stade du Hameau in their European Challenge Cup opener.
The English side were outscored by three tries to one, with Romain Buros, Sean Dougall and Watisoni Votu all crossing for the hosts, but Priestland's boot proved decisive as Todd Blackadder's men held on despite losing Aled Brew to a late yellow card.
Another Welshman in fine kicking form was Gloucester's James Hook, who contributed 17 points with the boot as his side enjoyed an altogether more comfortable 47-27 win in their Pool 1 clash with Top 14 strugglers Bayonne.
England wing Jonny May marked his return from 10 months out with a knee injury by scoring one of the visitors' six tries, with Mark Atkinson, Matt Scott, Billy Twelvetrees and Tom Savage also finding the line for Gloucester, who had replacement prop Motu Matu'u sin-binned in the second half for pulling down a maul.
The other game in Pool 1 saw La Rochelle ease to a 41-10 win at Benetton Treviso, with France prop Uini Atonio scoring two of their five tries.
In Pool 3, meanwhile, Worcester failed to make it a hat-trick of English victories as they slumped to a surprise 19-12 defeat the hands of Enisei-STM in Moscow.
The Russian side, who also upset Newcastle and Brive last season, claimed a third notable scalp courtesy of a try from Davit Kacharava, three penalties and a conversion from Yury Kushnarev and a late Ramil Gaisin drop-goal.
Josh Adams and Derrick Appiah both claimed five-pointers for the visitors.
But there were no such problems on their travels for Edinburgh, who breezed to a resounding 59-17 victory over Timisoara Saracens in Romania.
The first of the Scottish side's nine tries arrived after just two minutes, with skipper Stuart McInally and back-rower Nasi Manu eventually claiming hat-tricks.