Leicester director of rugby Richard Cockerill slammed his side for "embarrassing" defensive lapses in their 23-16 home defeat by Harlequins.
The Aviva Premiership champions slipped off too many tackles and were dominated by a Harlequins side who outscored them two tries to one and also leapfrogged them in the table to go fifth.
It was Harlequins' fourth win in six visits to Welford Road and Leicester have now won just one of their last five games in all competitions.
Cockerill said: "If people run at you and you don't tackle them they win, and that's what happened.
"You have got to defend better than that, certainly in the first half. The sin-binning hurt us, they scored two tries in that period.
"But they ran hard and we did not get off the line and make our tackles. We let them play and they played very well and deserved to win. They wanted it more than us.
"We rallied well and that is great but you can't get yourself in that position in the first place.
"They outplayed us. I am not going to accept that, that is not good enough for us.
"Some of our defence early in the game was embarrassing. They will see it on Monday, and we have to be better."
Harlequins' two tries came from captain Nick Easter and centre Matt Hopper either side of half-time while Leicester flanker Julian Salvi was in the sin-bin.
Nick Evans, playing out of position at full-back, kicked 13 points, while Leicester earned a penalty try in the 80th minute and fly-half Owen Williams kicked 11 points.
Harlequins director of rugby Connor O'Shea praised his players for the way they played in a difficult wind and rain and said winning the toss was crucial.
He said: "We talked about the opening two minutes. We wanted to play into the wind and when you do that you are forced to play.
"Chris Robshaw never wins the toss, Nick Easter has won the last two so he is going to do the toss every time now.
"We played that opening two minutes exceptionally well, it showed we could play our own game."
O'Shea also praised former England No.8 Easter, who played out of position at lock, and thinks the 35-year-old can still add to his 47 caps.
He said: "How many times have I said that he will be younger by the time of the World Cup than Brad Thorn who won a World Cup winner's medal.
"He is so competitive it is ridiculous. You can't write off someone like that, he will continue playing until he drops."