The Foxes manager was left seething with referee Darren Deadman after he sent off Matty James and failed to see what appeared to be a foul on goalkeeper Kasper Schmeichel for Charlton's second goal.
Former City striker Yann Kermorgant scored twice last season against his old team and he repeated the trick on Saturday to add to Michael Morrison's early opener.
Despite Danny Drinkwater's strike Charlton held on to secure a 2-1 win, much to Pearson's frustration.
"There were certain things we were a bit disappointed with," he said.
"In the first-half we didn't find our rhythm and were slow to do things. We looked comfortable besides set-pieces.
"In terms of our own performance we were not at our best.
"But we could have got something out of the game. We pushed on, even with 10 men, but it wasn't to be.
"We didn't show the energy I would have liked. Unfortunately the talking points are not the players.
"The second goal was an absolute foul on Kasper. Liam Moore was also fouled. It was a foul on Matt, whether it is inside or out of the box is irrelevant.
"I had a very good view so the assistant has an excellent view but had no input.
"We have been told what the second yellow card is for and will wait for the report. We will see if there is any conflict on those two explanations."
Charlton drew first blood after Morrison headed in Dale Stephens' 27th minute corner.
With Leicester trailing, James looked to have been shoved over for a penalty and he took his protests too far when Deadman pulled out a second yellow card with 52 minutes on the clock.
It would get even worse for the visitors seven minutes later when Kermorgant rose to nod in Johnnie Jackson's corner, as Schmeichel's protests were waved away.
Drinkwater threw Leicester a lifeline three minutes later but it was not enough.
Charlton manager Chris Powell said: "I'm pleased for my group of players.
"They have been down and it is tough start but I told them there was no need to panic.
"We've had a lot of soul-searching between us all, a lot of hard work of the training pitch and changed our shape which has worked."
He added: "When Yann plays like he does today then not many strikers are better than him.
"I'm going to tell him there are 23 other teams called Leicester.
"He is good in the air, on the ground and he sees other things people don't.
"He has now played against them three times and scores three times. It is pleasing for him as he had rough time there.
"I was there with him as a coach so I knew he was a good player and that's why I brought him in. It was a good day for him and us."