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.
"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 said.

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