Gloucester 31-41 Biarritz
Gloucester were made to pay for their indiscipline as Amiln Challenge Cup holders Biarritz reached the last four.
A Mike Tindall try put the home side ahead but the French side scored 24 points while Dario Chistolini and then Koree Britton were in the sin-bin.
Dimitri Yachvili converted three tries while Damien Traille dropped a goal to put Biarritz 27-14 ahead at half-time.
Benoit Baby and Seremaia Burotu stretched the lead before Shane Monahan and Huia Edmonds' consolation scores.