David Nugent's first-half strike gave Portsmouth a 1-0 victory at the Walkers Stadium and seriously dented Leicester's push for a top-six finish in the npower Championship.
Nugent's 11th league goal of the season provided Portsmouth with a welcome away win which moves them to a point behind the Foxes in mid-table. With eight games remaining, Leicester stand five points outside the play-offs.
Sven-Goran Eriksson's home side dominated for large periods of the game but could not find an equaliser as a dogged defensive performance from Portsmouth saw Steve Cotterill's troops claim their eighth clean sheet in nine matches.
The visitors opened the scoring against the run of play after 13 minutes when Sol Bamba's poor defensive header landed at the feet of Nugent and the striker made no mistake, firing into the bottom corner from 12 yards.
Eriksson's side were infuriated after 55 minutes when Gallagher's free-kick looked to have hit a visiting player`s hand but the referee waved away the protests.
Eriksson threw on Lloyd Dyer and Martyn Waghorn to try to find an equaliser but it was Portsmouth who had a great chance 10 minutes from time. Joel Ward fluffed his finish from close range after Bamba looked for an offside flag.