Mauricio Pochettino was "angry and disappointed" after watching Chelsea fall apart in their 4-1 Premier League defeat at Newcastle.
The Argentinian was left furious by his side's second-half capitulation at St James' Park, which saw full-back Reece James sent off to erase the memories of their creditable displays against Tottenham and Manchester City before the international break.
Pochettino, who watched the game from the directors' box as he served a touchline ban, said: "We didn't prepare ourselves in the best way to compete today, that is my concern.
"We thought that we were ready to compete today, but we didn't in the way that the competition demands.
"Even if Newcastle weren't great, it was an easy win to prepare for the Champions League today. We had to come here, Chelsea, to show that it's going to be difficult for them to play, to win the game and to beat us.
"But it was really easy in the way that we conceded and the way that we were so soft in every single challenge. We didn't show that we were playing for something important.
"That's what makes me angry and disappointed. We talk about that we are a young team and we have to learn, but I think these type of games make me very, very, very, very, very angry because it's about showing your personality and character.
"Okay, we are young as a team, but we cannot lose this type of opportunity to show our best."
Newcastle had 13 players missing after midfielder Joe Willock had been added to the casualty list with a recurrence of an Achilles injury.
But the hosts took a 13th-minute lead when Alexander Isak, back after a month out, span on 17-year-old Lewis Miley's astute pass and fired past Robert Sanchez.
The visitors levelled before the break courtesy of Raheem Sterling's sweetly-struck free-kick, only to succumb to goals from Lascelles and Joelinton within three second-half minutes and a fourth from Anthony Gordon after James had picked up a second booking.
Magpies head coach Eddie Howe, who now faces the tasking of preparing his injury-ravaged side for Tuesday night's Champions League trip to Paris St Germain, was delighted with the resilience his players showed in adversity.
Howe said: "It's such an important win for us with the position we're in, the stretched resources that we have.
"To be able to come together and give a performance like that speaks volumes for the character of the players we have, the leaders we have in the group and our ability to just focus on the present, on what's happening right now.
"You look at the players who were missing and that was a giant performance from the players we have fit."
However, Howe's enjoyment was tempered by Willock's misfortune with the player and his club awaiting a prognosis.
He said: "It looks like a recurrence of an Achilles injury that he had a few weeks ago. It's a massive blow for us.
"We don't know how long he's going to be out, we're going to have to seek specialist advice, but it's a huge blow for us."
