Bath boss Steve Meehan claimed his team needed to "grow up" after their Heineken Cup campaign began in frustrating fashion against Biarritz at the Recreation Ground.
Biarritz marksman Dimitri Yachvili punished Bath's indiscipline by kicking four penalties - the last one 10 minutes from time after home prop David Wilson was sin-binned - to clinch a 12-11 Pool Four verdict.
"It's actually quite difficult to put into words," said head coach Meehan. "We played a very good first half - we got all the decisions right - but a few technical penalties went against us in the second half. And then with four minutes to go, we had an opportunity to win the match, but we didn't take it."
Bath had opportunities to give Barkley a late drop-goal chance, but they proved tactically naive under pressure and Biarritz possessed the nous to close out a disappointing game.
Meehan added: "Biarritz were happy to live off our penalties to begin with in the second half. They ticked over three points at a time.
"We've got to grow up and take the points. It's straightforward, it is about being ruthless, getting the job done and getting it (the ball) through the sticks. Simple.
"Drop-goals and penalties win games. They (Biarritz) kick the penalties and keep the scoreboard ticking over. We had the opportunity and didn't take it."
As for England international Wilson's sin-binning, Meehan added: "Anyone who gets yellow-carded frustrates himself, the coaches and the team. We have given away too many yellow cards already this season.
"When we are doing things on the field the way we do in training, we are a very good side.
"We have got to transfer more of that into games."