Glasgow's Heineken man of the match John Beattie admitted his bitter disappointment at defeat to Biarritz in Pool 4.
The Scottish side were minutes away from completing an historic double over the French side following last weekend's 9-3 win at Firhill but found themselves truding into the changing rooms in sombre mood.
Leading 9-14 with less than three minutes of normal time remaining, Warriors legs tired and replacement forward Samiu Vahafolau crossed twice to see his side home.
The win means Glasgow are third in the Pool with 11 points from their four games played, a far cry from the position they would have been in had they been able to hold on for a few minutes longer.
And Beattie knew it. "After so much effort it's really tough to end up on the losing side tonight," he said.
"We're under no illusions as to hard it is to get out of this pool and we've made it a lot tougher for ourselves.
"We have been working really hard on our defence and are really proud of it. Unfortunately we couldn't shut them out in the end. We're bitterly disappointed in the changing rooms.