Croatian star Robert Prosinecki came up with the vital goal to lift Portsmouth out of the gloom and increase Forest's New Year woe.
Pompey, with eight defeats in their previous nine games, were heading for stalemate against a Forest side who themselves have yet to win in 2002.
But seven minutes from the end Prosinecki struck with a 22-yard free kick after Forest defender Jon Hjelde had brought down Kevin Harper.
Prosinecki, looking for a touch of class, got a slice of good fortune instead as his effort took a deflection off the Forest wall and left goal keeper Darren Ward stranded.
It was a goal that Portsmouth had threatened, particularly in the first half when they created much the better chances.
Prosinecki, himself, was guilty of a wasted opportunity in the 15th minute.
He was fed by Gary O'Neil and shot straight at Ward with only the goal keeper to beat from 15 yards.
Portsmouth got nearer still when Ward fumbled a Prosinecki corner and Lewis Buxton prodded the loose ball against the foot of the post.
Next it was the turn of big defender Linvoy Primus to spurn a chance, heading wide after being picked out unmarked from yet another Prosinecki delivery.
Forest were not without openings themselves and Marlon Harewood volleyed wide in the early stages from a superb cross from Tony Vaughan.
The second half went much the same way and the deadlock looked set to be broken in the 51st minute when Harewood pounced on a cross from England Under-21 star David Prutton.
But with Harewood ready to celebrate, he was denied by a stunning save from ex-Forest goalkeeper Dave Beasant.
Beasant then escaped without conceding a penalty after sending Harewood sprawling in the box - the Forest player instead getting a yellow card for diving.
Portsmouth defeat Nottm Forest in our trip to City Ground. Review the information and discuss it on the messageboard.