Jose Mourinho accused his Chelsea players of betraying his work after Leicester City handed the Premier League champions their ninth league defeat of the season at King Power Stadium on Monday.
Goals from Jamie Vardy and Riyad Mahrez on either side of half-time were enough to take Claudio Ranieri's side back to the top of the table and leave Chelsea, who pulled one back through Loic Remy on 77 minutes, just one point above the relegation zone after 16 matches.
Speaking candidly after the match, Mourinho said he held his players responsible for not heeding his tactical instructions on the night.
"I think [Leicester] deserve to win because they were better than us during a longer period of time," the Chelsea boss told Sky Sports. "We were the best team for 20, 25 minutes, maximum half an hour. They were the best team for about an hour, very consistent, very focused not making mistakes, aggressive with everybody playing high intensity, high tempo; great mentality and difficult for us.
"Then we concede two goals that are unacceptable for me, because I know one of my best qualities is to read the game for my players, to read the opponent, to identify every detail about the opponent.
"These two goals, the movement of Vardy between the two centre-backs, the cross with the left foot, where we have one-against-one that I want one-against-two, because I want a midfielder to come and help, are two goals very difficult to accept, a big frustration to accept because I feel like my work was betrayed."
The result is simply the latest setback in what has been a remarkable fall for Chelsea after claiming the club's first Premier League title in five years, and Mourinho, whose future at Stamford Bridge is subject to intense speculation, questioned whether his players overachieved last season.
"All last season I did phenomenal work and I brought them to a level that is not their level, is more than they really are, or this season we are doing so bad that the players for some reason -- I'm not saying all of them, I don't want to put some of them in the same basket -- but some of them it's so, so difficult," he said.
Chelsea suffered an early blow at King Power Stadium when Eden Hazard limped out of the match on 31 minutes after a late challenge by Vardy, and Mourinho admitted he never found out the extent of the problem before the Belgian left the field.
"The only thing I know is in 10 seconds, he made the decision himself," Mourinho said. "It must be a serious injury because he just left the pitch and just made the decision not to go in.
"His first reaction was 'I can't,' and I was going to make the change. His second reaction was 'I want to try,' and when he goes on the pitch, first step he immediately says 'I can't do it.' It was him in a few seconds who had three different perspectives, but clearly he couldn't do it."
Mourinho conceded that Chelsea's ninth defeat of the season ends their hopes of finishing in the top four and revealed he is unsure of how to steer his team out of their prolonged slump.
"I don't know another way than work at the top level, which is what I do every day," he said. "And again, I have to be honest and say that day by day in training, I have no complaints with the players.
"If I look at some matches and feel frustrated with the difference between what they do in training and what they do in matches, clearly yes.
"But I have to be honest with the players and say every day I enjoy to work with them because they want to work."
Asked if the defeat meant anything for his future as Chelsea manager, Mourinho told the BBC that nothing had changed.
"The last question [about my future] is always the same," he said. "The only thing I can say is that I want to be the manager. I have no doubts and I think you know me well enough to know that I am not afraid of a big challenge, and in this moment it is a really big challenge.
"I want to stay, and I hope [owner Roman] Abramovich and the board want me to stay because I want to stay."
Mourinho did say a Europa League spot was possible despite Chelsea's shameful start to the campaign.
"We can't finish top-four, but we can still finish top-six because so many teams are dropping points," he told BBC Sport. "But at the moment, we're in a zone where I feel ashamed."