Nugent spoiled Michael Appleton's first home game in charge of Pompey on Saturday.
Nigel Pearson's side had to do it the hard way, falling behind to a David Norris strike before Nugent popped up to earn the Foxes a deserved point with his sixth goal of the season.
The visitors never looked likely to suffer the same humiliation which befell them in last season's corresponding fixture, when Pompey ran out emphatic 6-1 winners.
In fact they started the game much the brighter, evidently drawing confidence from the 3-0 win over Crystal Palace which marked Pearson's return to the helm.
Greg Halford's foul on Lloyd Dyer gave the away side an opportunity to get the ball in the box early on, but Dyer's delivery was easily cleared.
Moments later Paul Gallagher tried to play in Jermaine Beckford but Stephen Henderson was quick off the mark to end the danger, while Norris fired a long-range shot wide for the hosts.
Lee Peltier dragged his shot narrowly wide from inside the box with the best chance of the half after just eight minutes.
Midway through the half, Dyer crossed low for Nugent at the far post but his shot was stabbed wide.
The hosts were thwarted by an offside flag 10 minutes before the break as Joel Ward looked to latch on to Dave Kitson's measured pass.
Gallagher fired a free-kick just over the bar from 35 yards as the away side finished the first half on top.
Pompey raced out of the blocks after the interval and Kitson's close-range header from a Norris cross brought a stunning save from Kasper Schmeichel, who miraculously denied the former Reading striker.
Nugent and Gallagher linked well as Pearson's men mounted a response, but Hayden Mullins, making his 500th career league appearance, was alert to the danger and he muscled in to clear the danger.
But just as the away side were beginning to build up a head of steam, they masterminded their own downfall with a sloppy piece of play after 68 minutes.
They sloppily conceded possession and the ball fell kindly for Norris, whose deflected shot deceived Schmeichel and landed in the back of the net.
It took just six minutes for Leicester to put that disappointment behind them as Nugent's 20-yard shot levelled the scores.
The celebrations on the away bench had barely finished when Norris almost brought them to an abrupt end, firing a powerful effort against the bar.
At the other end, Dyer's teasing cross into the box eluded everyone and drifted away to safety as the match ended honours even.