Wasps' European challenge was brought to a shuddering halt by a deserved Harlequins victory, according to director of rugby Dai Young.
Wasps led 21-0 and then 28-12 but Harlequins fought back to win 33-28 in the Champions Cup thanks to James Chisholm's last-minute try.
Wasps now trail Pool 1 leaders Ulster, who they face next week in the final round of pool matches, by five points and La Rochelle by four points and, while mathematically they can still qualify for the quarter-finals, Young believes the club's European ambitions are over for this season.
"We got what we deserved," Young said. "We probably won that game three times and let them back in there really, so there were some really poor errors which obviously gave them a little bit of momentum and we were just not good enough in defence really. But you know, we showed some quality but not enough fight.
"And fair play to Quins, they showed more fight on the day and they wanted it a little bit more than us in the end, which is hugely disappointing and it really irks me to say that but I honestly believe that. I think it's over."
Wasps surged into a 21-0 lead after the half-hour mark and Harlequins looked dead and buried before they got a foothold in the game through tries from Ross Chisholm and James Lang.
Later, Marcus Smith entered to continue a momentum that eventually overwhelmed Wasps with scores from Danny Care, Elia Elia and James Chisholm.
"We felt that we had to win two games and it won't change our mindset next week," said Young.
"We want to win to finish strongly [against Ulster] but we are hugely disappointed and we've only got ourselves to blame because as I say we were in a position to win that game and win it comfortably, but we didn't show enough desire in defence to hold them out really.
"Pretty much over the last three or four games its been exactly the same really, we're scoring four or five tries and we are letting four or five tries in.
"And I've said it the last couple of weeks - at some point it's going to go the other way for us. We are winning games comfortably but we are letting teams score far too easy points.
"Tonight was further evidence of that and if you are going to win something you've got to shore your defence up and we're not good enough in that area at the minute."