Leicester owed victory as much to goalkeeper Chris Weale's brilliant fingertip save to deny Boro substitute Mark Yeates' goalbound shot in the closing stages, but the Teessiders have only themselves to blame for taking just one point from their last three matches.
Neither side troubled the opposition goalkeeper in an uneventful first half.
Matt Oakley's early effort was blocked by Boro's Sean St Ledger, in his third game for Gareth Southgate's side, and the former Preston defender later hurled himself in front of efforts from Lloyd Dyer and Matt Oakley to avert any danger.
Middlesbrough midfielder Julio Arca fired over the crossbar from 25 yards early on, team-mate Jeremie Aliadiere saw his shot from similar distance comfortably held by Leicester goalkeeper Chris Weale and a Marvin Emnes drive was charged down by visiting defender Jack Hobbs.
Middlesbrough had made just one change, with defender Justin Hoyte (ankle) replaced by Tony McMahon, while Leicester drafted in five new faces from the side that started in the home defeat to Preston on Saturday.
Defenders Hobbs and Michael Morrison, midfielders Andy King and Dyer and French striker Yann Kermorgant, making his full debut, were all promoted to the starting line-up.
Boro went on the offensive early in the second half. Aliadiere's header from McMahon's cross was neatly gathered by Weale, defender Joe Bennett failed to connect properly with his 30-yard shot and Emnes dragged his angled drive wide.
Southgate made a double substitution just after the hour in a bid to invigorate his side, sending on midfielder Mark Yeates and striker Leroy Lita for Arca and Emnes.
Pearson responded with two positive substitutions of his own, with strikers Martyn Waghorn and Steve Howard replacing Matty Fryatt and Kermorgant.
Yeates made an instant impression when his free-kick was met by centre-half David Wheater, who headed powerfully into visiting goalkeeper Weale's hands from 12 yards.
Yeates then pulled a 25-yard shot wide and then curled a better effort just beyond Weale's left-hand post as the home side pressed for the breakthrough.
But with seven minutes remaining Leicester stunned most in a crowd of 18,577. Oakley's ball into the penalty area spun kindly to Dyer and the midfielder thumped it into the bottom corner from 12 yards.
Boro went in search of a late equaliser, but when Yeates crashed his volley from Gary O'Neil's cross towards the top corner, Weale leapt high to his right to push the ball away for a corner.