The Blues were beaten for the fifth Premier League game in a row on Tuesday (21.04.26) and the coach was left feeling "numb" and "angry" after witnessing his side's abject display.
Rosenior told Sky Sports: "It is unacceptable, in every aspect of the game. I keep coming out and defending the players, that was indefensible, that performance tonight. The manner of the goals we conceded, the duels that we lost. Something has to change drastically right here, right now.
"We need to look in the mirror. I need to look in the mirror. But I can't keep coming out here and defending some of the things that we're seeing. Manchester United [last weekend], genuinely the result wasn't there but I felt we turned a corner.
"But the general attitude, the spirit was lacking - determination wasn’t there apart from three or four of the starting eleven. That's nowhere near enough for this club. I can't come out and lie. I tell the truth. That was an unacceptable performance at every level."
Rosenior - who was subjected to abusive chants from furious Chelsea supporters - said that the defeat was one of the worst moments of his managerial career so far.
He said: "The performance in terms of professionalism wasn't there. It was a really, really difficult night, the most difficult night - not even here at this magnificent football club - but in my career. Some of the things I witnessed today, I don't want to ever see again.
"If you're playing at this elite football club, or any football club, to be even accused of throwing the towel in is unacceptable. That's all I'm going to say. I'm hurting, I'm feeling numb. That doesn't represent me. That doesn't represent the football club in any way. That has to change."
The coach felt that his players lacked "desire, spirit and courage" during the loss.
Rosenior said: "I will look at the team, will look at individuals and I will look at a team I can trust to do the basics of football and we should not be talking about the basics of football at this level. It is something we have to adjust very quickly.
"Tonight was not [about] tactical. This was about desire, spirit, courage and I did not see enough of that tonight. Nowhere near good enough and we have to improve that."
