Goals at either end of the first-half from Britt Assombalonga gave Forest the victory at Portman Road.
The former Peterborough striker capitalised on slack defending from kick-off to give his side the lead and then just before the break was first to the loose ball to extend the advantage.
David McGoldrick and Tom Lawrence both went close to reducing the arrears and Blues did enough in the second-half to have got back in the game but couldn’t find a way past Vladimir Stojkovic in the Forest goal.
Town got off to the worst possible start, Ben Osborn sliding in Assombalonga who buried his shot into the far corner past Bart Bialkowski with just 17 seconds on the clock.
Pajtim Kasami tested Bialkowski immediately with a volley as Forest threatened a second, Town responding with Freddie Sears trying to play in McGoldrick.
Assombalonga forced Bialkowski into action again with a free-kick that took a deflection, then Kasami had the Town ‘keeper scampering to his left to make another save.
Tom Lawrence sent a dipping free-kick wide, Christophe Berra forcing a corner with a neat turn and run on the edge of the box as Blues began to grow into the game.
Bialkowski did well to claim Eric Lichaj’s cross at full stretch with Assombalonga ready to pounce at the far post, the Town ‘keeper then holding firm to hold from Thomas Lam’s driven cross.
A terrific run from McGoldrick would have conjured up an equaliser for Town on the half hour if Stojkovic hadn’t stuck out his right hand to divert the ball past the post.
Damien Perquis had a header cleared off the line from a corner, Stojkovic quickly off his line to prevent Grant Ward getting on the end of McGoldrick’s header.
Just before the break, Assombalonga made it two to the visitors, Matt Mills heading the ball on and the Forest hitman was quickest to react to head in from four yards.
Town made a double change at half-time, with Kevin Bru and Jonny Williams on for Ward and Teddy Bishop.
The two substitutes immediately made an impact, linking up well with Williams’ cross bundled behind for a corner.
Williams then fed Sears, with Lawrence crowded out as he tried to force the cross home from close range.
Forest continued to carry a threat though and Bialkowski beat out Henri Lansbury’s effort from the edge of the box.
Williams almost found McGoldrick with an incisive pass, the Wales international driving Town forward every time he received the ball.
Assombalonga, who appeared to be carrying a knock, made way for Apostolos Vellios, who was immediately booked for a foul on McGoldrick.
Berra stayed strong to clear the danger as Vellios took him on in a one on one on goal, McGoldrick then testing Stojkovic from 25 yards.
Michael Mancienne replaced Daniel Pinillos just past the hour and seconds later Forest were a coat of paint away from grabbing a third, with Kasami smacking the post from 15 yards.
Bru found Sears with a neat pass inside the Forest box as Town looked for a lifeline but Mills cleared the danger, before Luke Varney replaced Josh Emmanuel in Blues’ final throw of the dice.
Lawrence dragged his shot just wide after an incisive run, Berra getting on the end of a free-kick from the Scotland international but Stojkovic held on.
Lawrence went down under a challenge inside the box from Mancienne as Town pegged Forest back but referee Peter Bankes waved away the penalty appeals, Sears then denied as he looked to strike from close range.
Bialkowski held on from Vellios’ shot as Forest broke. Lawrence going down again in the box but again no penalty.
Forest held on though for their first away win of the season in the Championship, as Blues inconsistent form continued.
Town: Bialkowski, Emmanuel (Varney 69), Chambers, Berra, Knudsen, Skuse, Bishop (Williams 46), Lawrence, Ward (Bru 46), Sears, McGoldrick. Subs not used: Gerken, Kenlock, Douglas, Dozzell. Booked: McGoldrick.
Nott'm Forest: Stojkovic, Lichaj, Pinillos (Mancienne 62), Mills, Assombalonga (Vellios 55), Lansbury, Osborn, Kasami, Perquis, Lam (Grant 85), Worrall. Subs not used: Henderson, Dumitru, Carayol, Lica. Booked: Vellios, Lansbury.
Att: 15, 417