The champions have now lost nine of their 16 league games and stand one point above the relegation zone in 16th place after goals from Leicester's Jamie Vardy and Riyad Mahrez condemned the visitors to another painful defeat.
Vardy volleyed home Mahrez's precise right-wing cross after 34 minutes and Algeria forward Mahrez teased Cesar Azpilicueta on the right side of the area before curling a sublime left-foot shot into the far corner three minutes after the break.
"We conceded two goals that were unacceptable for me because I know one of my best qualities is to read the game for my players, to read the opponents, to identify every detail about the opponent and these two goals..." said Mourinho.
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"The movement of Vardy between the two central defenders, the cross with the left (foot by Mahrez), then Mahrez in the box, one against one that I want one against two because I want the midfield player to close the best foot (of Mahrez).
"They are two goals (that are) very difficult to accept, big frustration to accept, because I feel like my work was betrayed if it's the right word," Mourinho told Sky Sports.
"All last season I did phenomenal work and I brought them (Chelsea's players) to a level that is not their level, that 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 of course, I don't want to put some of them in the same basket -- but clearly with some of them it's so difficult."
Mourinho injected some life into his deflated side by bringing on Loic Remy for midfielder Oscar after 65 minutes and the Frenchman delivered a goal 12 minutes later from a cross by fellow substitute Pedro but Chelsea could not find an equaliser.
The result has left the champions 14 points outside the Champions League places, and 20 behind Leicester, leaving Mourinho to repeat his view that Chelsea won't qualify for Europe's elite club competition via their league placing.
"We can't finish top four, but we can still finish top six because so many teams are dropping points," he told the BBC.
"But at the moment we're in a zone where I feel ashamed."
"I accept we are in the relegation zone but I don't accept we are in a relegation battle," the Portuguese coach told a post-match news conference.
"You look at the table and we are there but you think you are in a relegation battle if you think you are there for three or four months. I don't think that."
(Writing by Ken Ferris; Editing by Ian Ransom)
