Mauricio Pochettino accused Tottenham's players of arrogance and complacency after they threw away a lead to lose 2-1 at relegation-threatened Southampton.
Spurs, buoyed by the news their new stadium will open early next month, dominated the opening period at St Mary's and went ahead through Harry Kane's 200th career goal for club and country.
But quick-fire goals from Saints pair Yan Valery and James Ward-Prowse in the final 15 minutes dented Spurs' top-four ambitions, while keeping the struggling hosts out of the drop zone.
Manager Pochettino, who watched from the stands as he began a two-match touchline ban, was angered by an alarming second-half display which came on the back of reaching the Champions League quarter-finals in midweek.
"We showed a lack of aggressiveness, lack of the hunger that you need to kill the games and win," said the Argentinian.
"We played the first half like (one of) the best eight teams in Europe but in the second half we need to watch the game, we need to analyse and we need to be critics with ourselves.
"I am so, so, so disappointed.
"I am a little bit worried about this change from the first half to the second half – it's only one thing, it's mental.
"It's about complacency, it's about arrogance in a bad way.
"You can use the first half as an example of (positive) arrogance, playing with intention, focus, concentration, we matched them in everything and we were much better.
"And in the second half it's the arrogance in a bad way. We need to blame all of us, the club."
With the prospect of returning to White Hart Lane prompting chants of "We're going home" from the large travelling support, it looked like being a memorable afternoon for the visitors after Kane's eighth goal in nine games against Southampton.
But they paid the price for only taking a slender advantage into the break.
The result is a fourth successive top-flight game without victory for Spurs and leaves them anxiously looking over their shoulders at Manchester United, Arsenal and Chelsea in the race for Champions League qualification.
Pochettino felt the setback on the south coast highlighted the club's deficiencies and provided a reality check in their quest to earn a place among Europe's elite.
"I think it's good now (that we're in a battle for the top four) that people now are going to realise our real level and maybe stop with the perception," he continued.
"That showed that we still have a lot of work to do, that showed we are not mature enough, that showed that to be in the last level you need more effort, you need more quality, to increase your capacity of commitment.
"Everything you need to increase if you want to be one of the best clubs in the world.
"We need to be careful how we assess ourselves and it's so important to live in the reality. I think in the last few years we were living more in the perception than in the reality and now is the reality."
After fellow strugglers Cardiff beat West Ham, Saints' success ensured they remain two points above the bottom three.
Southampton manager Ralph Hasenhuttl felt his players used the disappointment of last weekend's late loss at Manchester United to secure a significant step towards safety.
"The good thing was we were only one goal down, that gave us the chance to change a few things and to force a little nervousness and put them out of their comfort zone because Tottenham were amazing (in the first half)," said the Austrian.
"We lost against Man United after a really sensational game we played there. And we only earned warm words and I said to them we want to earn more than only warm words, we want to earn points.
"That's what the crowd felt in the second half, that there's a team on the pitch fighting for every point and that was a moment to celebrate with them but also to tell them that it's only one step, a big one maybe.
"But, as you see with the other results, we have still wins to take and a long way to go."
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