Leicester striker David Nugent scored an equaliser against his former club to spoil Michael Appleton's first home game as Portsmouth manager.
The visitors had the best chance of the first half as Lee Peltier dragged his shot wide from inside the box.
David Norris put Portsmouth ahead with a deflected strike in the 68th minute, but Nugent's impressive 20-yard shot levelled matters six minutes later.
Norris then struck the bar with a powerful effort as Leicester held on.
Nigel Pearson's side had started the game well with Peltier's chance being followed by another good opening, as Lloyd Dyer crossed for Nugent, who stabbed the ball wide.
Paul Gallagher then fired a free-kick just over the bar from 35 yards as Leicester finished the first half on top.
Portsmouth raced out of the blocks after the interval and Dave Kitson's close-range header from a Norris cross brought a stunning save from Kasper Schmeichel.
Just as the away side were building up a head of steam again, they caused their own downfall with a sloppy piece of play. They conceded possession cheaply and the ball fell kindly for Norris, whose deflected shot deceived Schmeichel.
Nugent quickly made amends with his strike before Leicester survived Norris's chance.