The Blues failed to build on their weekend victory over Fulham as two first half goals from the Foxes inflicted their sixth defeat of the season.
The hosts started on the front foot and took the lead with a stunner from Wilfred Ndidi on the edge of the area inside the opening six minutes.
James Maddison got the Foxes’ second goal four minutes before halftime and that was enough to beat a lethargic Chelsea side that lacked spark throughout the game.
"Beaten by the better team. They were sharper than us, ran more than us and they looked in form - we looked out of form. Disappointing goal from a set piece and the second goal is just not good enough,” Lampard said after the game.
"There were quite a lot of moments where our sharpness wasn't there, those are moments you have to dig in and the basics are important like running and sprinting and we didn't do that.
"The most disappointing thing is to come here and lose the game but the basics off the ball are important.
“The game on the ball was a bit slow at times but it was okay, we created a few opportunities and I thought it was a penalty but I'm not going to lean on those things. We weren't good enough.
"We won against Fulham without playing brilliant, from that we come and lose a game so it's a small step backwards.
"I am worried about the slump - from the form we were in to get so quickly into the form we're now in and we've had some wins but five losses in eight isn't where we want to be.
“ It takes character to get out of that - I'm not against the lads in the dressing room because they're disappointed.
“It's a young team and it's a big lesson that if you come off it and think you're fine then you've got to get yourself out of the hole."
