An unfortunate own goal from Damien Delaney just before the break gave Forest the points at Portman Road.
The Republic of Ireland international diverted the ball over the line from close range after Marton Fulop could only beat out David McGoldrick's cross.
Troy Brown and Grant Leadbitter were both denied by Lee Camp in a game of few clear cut chances with the defeat leavings Blues just a handful of points above the drop zone.
Town also finished the game with 10 men following a red card in the last minute for Grant Leadbitter after a challenge on Paul Anderson.
Roy Keane made five changes to the team that drew at Coventry at the weekend. Connor Wickham was handed his first start in almost two months, with Delaney, Mark Kennedy, Jake Livermore and Brown also coming into the side.
Wickham forced a corner with a strong run down the right flank inside the first five minutes, Jack Colback then having the first shot of an even opening 45 minutes, Lee Camp making a comfortable save.
Rory Fallon had a penalty claim turned down after appearing to be impeded by Luke Chambers on the quarter hour, while at the other end Marton Fulop did well to clear Chris Cohen's dangerous cross with his feet, the 'keeper unsighted until the last moment.
Fulop saved more comfortably from Paul Anderson's header, Town then conjuring up the best move of the first-half, David Norris realising Wickham and his cross was met by Fallon's head but he couldn't direct the ball away from Camp.
Anderson tested Fulop with another header, then Livermore fed Brown down the right and from his cross the ball broke to Norris but he blazed a left foot shot over.
Brown was denied by a Camp tip over from Leadbitter's corner on the half hour, Gareth McAuley heading wide from the resultant corner.
Camp and Norris entered referee Darren Sheldrake's book for timewasting and a foul, then it took a save low down from Fulop to deny Guy Moussi.
Leadbitter flashed a 30 yarder just over, Joel Lynch deflected a Forest free-kick just past the post before the visitors got the breakthrough out of nothing on the stroke of half-time.
McGoldrick escaped down the left, his cross was palmed out by Fulop but struck Delaney and rebounded over the line.
Town made a change at the break with McAuley, who made his return at Coventry after two months out with an achilles injury, replaced by Jaime Peters. Brown moved inside to partner Delaney.
Fallon couldn't get on the end of Leadbitter's free-kick, while Cohen blazed over at the other end as both sides made a tentative start to the second-half.
Jason Scotland and Carlos Edwards replaced Fallon and Livermore in an early double change, Edwards immediately forcing a corner.
McGoldrick flicked a header just wide as Forest threatened a decisive second goal while Town were almost level a minute later, a slick move involving Scotland and Wickham sent Norris into the box but his shot went inches wide of the far post.
Peters did superbly to toe poke the ball away from Anderson as he rounded Fulop inside the box, Edwards then forcing another corner as Chambers cleared his cross to safety with Scotland threatening.
Aaron Ramsey became the third player to be booked after a foul on Scotland, Fulop beating out McGoldrick's long range effort, the former Southampton striker then making way for Marcus Tudgay for the last 20 minutes.
A well worked corner set up Leadbitter to find Wickham at the far post but he couldn't keep his header down, Norris then taking a smash in the face from the ball as Lynch cleared.
Kelvin Wilson replaced Lynch for the last 10 minutes, Nathan Tyson then wasting a great chance to clinch the points, heading wide from Anderson's header back across goal.
Camp saved at full stretch from Leadbitter before Forest made a final change, Dele Adebola on for Tyson.
Forest held on through the five minutes of added on time with few alarms apart from Norris' left foot chip that sailed onto the roof of the net with Camp beaten.
Town's frustration was compounded by a red card to Leadbitter for a foul on Anderson that looked harsh but leaves the midfielder suspended for three games.
Town: Fulop, Brown, McAuley (Peters 46), Delaney, Kennedy, Norris, Livermore (Edwards 52), Leadbitter, Colback, Fallon (Scotland 52), Wickham. Subs not used: Lee-Barrett, Smith, Murray, O'Dea. Sent-off: Leadbitter. Booked: Norris
Forest: Camp, Gunter, Morgan, Chambers, Lynch (Wilson 81), Cohen, Moussi, Ramsey, Anderson, Tyson (Adebola 86), McGoldrick (Tudgay 71). Subs not used: Smith, McGugan, Earnshaw, Majewski. Booked: Camp, Ramsey.