Jim Mallinder admitted it was one of his worst nights in charge of Saints as Clermont crushed his men 37-5 at Stade Marcel Michelin.
The French side were 27-0 up at the break thanks to two tries from Noa Nakaitaci and one from Wesley Fofana.
Nick Abendanon stormed from his own 22 to score in the second half to compound Saints’ misery, with only a late Alex Waller score providing any consolation.
It was a humbling night for Mallinder’s men, up there with the 40-7 defeat to Leinster at Franklin’s Gardens in December, 2013.
And when asked whether it was one his worst experiences as Saints boss, the director of rugby said: “It’s one of them. I’ve had a few shockers and that’s definitely one of them.
“The disappointing thing is that you come into these games knowing you’ve got a chance, but knowing you’ve got to play to your very best. Today, we didn’t do that and therefore got well beaten.
“We talked about trying to make a good start, needing to make a good start and shut the crowd up, and completely the opposite happened.
“Clermont made a cracking start, put us under pressure and we really didn’t compete in the first half in any of the areas.
“Our set piece didn’t function, physicality wasn’t there, we couldn’t keep hold of the ball, spilled it too often and our kicking and kick chase was poor.
“We came up against a very good side - they played very well and we didn’t. If you go down 27-0 down at half-time, it’s game over.”