Boss Jim Mallinder felt basic errors cost Saints victory against Castres in Toulouse.
Mallinder’s men fell to a 21-16 defeat against the Top 14 side, who held on to claim their first four points in Heineken Cup pool 4.
Saints dominated the final stages of the game, but could only earn a losing bonus point through a late George Pisi try.
Castres went 10-0 up early on and didn’t pass up to opportunity to put Northampton to the sword, holding out for the win.
But Mallinder, though impressed with his side’s character, felt it would have been a different story had Saints got the basics right.
“We did well,” said the director of rugby. “It showed the character of the side to get a point, but I think we’re critical, as we always are, of our performance and we know if we’d have got those basic things right we’d have won the game and taken four points.
“We came back into the game quite strongly. In the second half we were getting that dominance up front, we were attacking well and if we’d have gone another 10 minutes there’s a good chance we’d have scored and won the game. But it wasn’t to be. We left ourselves too much to do.”
The refereeing of Alain Rolland was called into question after the game as Saints were left perplexed by some of his calls.
And Mallinder said: “The referee was refereeing in a different way than we’re used to in the Premiership, and that’s probably all I can say on it.”