Goals from Richard Keogh and Chris Martin put Derby in charge before Jeff Schlupp gave Leicester hope - but the home side weathered second-half pressure to move six points clear of the bottom three.
Pearson delivered a blunt assessment of his side's performance when he said: "We didn't play very well and we are in a bad run of form at the moment. That level of performance is not going to rectify it.
"There were too many mistakes. We didn't play with any authority in possession and conceded two poor goals. We huffed and puffed in the second half and had quite a lot of possession but didn't show the quality to rectify the situation.
"We have got to get back to basics during the international break because we have worked too hard to get ourselves in a decent position to put it in jeopardy.
"There are still opportunities left for us and we have to keep our nerve. One of the disappointments was that we have allowed the game to pass us by."
Derby manager Nigel Clough said: "It was probably the worst we've played at home this season in terms of the football we played but in terms of determination and sheer bloody-mindedness, that was as good a three points as we've had in the last few seasons.
"Our defending was a little bit better. We conceded one which we're not too happy with but I thought generally we had people throwing themselves at the ball on the edge of the box and the two centre halves were outstanding.
"The results before the game put us in a more precarious position than we would have liked so it's a relief for everybody. We should not be in this position - but we are."
Clough is hoping to keep Martin, whose loan spell from Norwich ended after the game, adding: "I think he wants to stay and that's the main thing."