A 70th-minute goal from David Nugent gave City their fourth league win in a row and sent Middlesbrough to a third consecutive defeat.
Foxes goalkeeper Kasper Schmeichel added to their misery by saving a penalty from Marvin Emnes in stoppage time.
"It is a good feeling to be second in the table and I thought the players applied themselves really well," said Pearson.
"We had a sneaky feeling that Middlesbrough would play the way they did with two wide players and no central strikers.
"It caused us a few problems tactically, but in the second half we pushed the full-backs forward and took a few more chances. But I thought we coped well and throughout the game created the better chances.
"It was a good game all round and there were one or two tight decisions, and Kasper made a fine save at the end from the penalty.
"Because of the weather it has been a tough day for the fans travelling to the match and for a lot of people. But we are very pleased with the result, as it is games like these which can define seasons. We have put ourselves in a good spot."