Northampton: Furbank (capt); Freeman, Litchfield, Dingwall, Ramm; Belleau, McParland; Fischetti, Wright, Green, Lockett, Van der Mescht, Kemeny, Pollock, Chick.
Replacements: Langdon, West, Kundiona, Prowse, Munga, Pearson, Weimann, Hutchinson.
Castres: Chabouni; Ambadiang, Botitu, Goodhue, Karawalevu; Herve, Fernandez; Walcker, Durand-Pradere, Corato, Ducat, Vanverberghe, Delaporte (capt), Ardron, Papalii.
Replacements: Colonna, Guerois-Galisson, Azar, Maravat, Cope, Ramototabua, Arata, Palis.
Yellow cards: Ambadiang (15), Ducat (18), Ramototabua (69)