Chelsea manager Jose Mourinho said that he felt "betrayed" by his players after they were beaten 2-1 by Leicester City.
The result moved Leicester back to the top of the Premier League but leaves Chelsea just one point off the relegation zone and a massive 20 points behind the Foxes.
The prolific Jamie Vardy, whose record run of 11 consecutive Premier League goals came to an end at Swansea City last weekend, beat goalkeeper Thibaut Courtois with a crisp volley from playmaker Riyad Mahrez's delightful cross after 34 minutes.
Algeria international Mahrez curled in a stunning second from the edge of the area three minutes into the second half to put Leicester.
Loic Remy gave the visitors hope with a close-range headed goal 13 minutes from time to set up a tense finish but the hosts held out to leave Chelsea mired in trouble.
"I am frustrated by the difference between training and matches. I have to be honest with them."
Mourinho admitted that Leicester were the better side and said: "I think they deserved to win because they were better than us during a long period of time.
"We conceded two goals that were unacceptable. One of my best qualities is to read the game for my players and I feel like my work was betrayed.
"It's obvious we did not play at our best level. Players in crucial positions are not at their normal level. It is hard.
"All last season I did phenomenal work and brought them to a level that is not their level and more than they really are... or this season we are doing so bad.
"Day by day in training, I have no complaints. I am frustrated by the difference between training and matches. I have to be honest with them."
Mourinho singled out Eden Hazard after the Belgian international appeared to hurt his hip after going to ground under a challenge from Vardy. Mourinho introduced Pedro when Hazard made it clear that he wouldn't be playing on.
On Hazard's injury, the Portuguese said: "In 10 seconds, Hazard made the decision to come off himself. It must be something serious."
Asked if Chelsea were out of the race for the top four, he replied: "Yes, clearly."
