Liam Trotter’s goal in added on time denied Town a first win at the City Ground since 1999.
The former Blue, on loan from Bolton and only signed this morning, stabbed the ball in from six yards out after Piotr Malarczyk had cleared off the line.
Jonathan Parr’s first goal of the season looked to have given Town the win when he struck 15 minutes from time, the Norway international hooking the ball high into the roof of the net from the angle.
Daryl Murphy and David McGoldrick both had chances to extend the lead but it looked enough until Trotter’s late, late strike.
Town made four changes to the side that lost at Hull in midweek, McGoldrick and Cole Skuse recovering from injury while Freddie Sears and Ainsley Maitland-Niles returned to the starting line-up.
Murphy, who struck twice in this fixture last season, had the first shot in anger after Jonas Knudsen’s cross had been half cleared, then Tommy Smith did well at the other end to stop Ryan Mendes getting in.
Mendes fired wide of the far post after former Blues' loanee Jonny Williams had led a Forest break before Town were forced into an early change, Knudsen replaced by Parr.
Christophe Berra headed clear from Jamie Ward’s cross in a first 25 minutes that brought only spasmodic forays into either penalty area, Berra holding firm again to deal with the threat from Nelson Oliveira.
The game came to life on the half hour when Mendes broke to set up Trotter and Dean Gerken produced a terrific save to his left to palm the ball away, the ‘keeper then deflecting Ward’s follow up effort behind.
McGoldrick, up against his former club, headed goalwards from a corner as Town responded, Kelvin Wilson hacking clear.
Gerken beat out Oliveira’s effort after dangerman Mendes had set him up, French wideman Mendes then firing into the sidenetting.
Maitland-Niles forced a corner in the last minute of the first-half but couldn’t make it count and from the break, Mendes rifled a shot just wide after Oliveira had fed him down the left.
Parr had a shot blocked by Wilson after Murphy had found him in the box, Ward then seeing his shot deflected over from 20 yards in a bright start to the second-half.
Kevin Bru and Sears linked up but the final pass went astray, Ward then blasting high and wide from the edge of the box.
Sears was denied by Dorus De Vries, the rebound fed back in by Parr but cleared, then Gerken got down well to smother Ward’s effort.
Town looked much more of a threat going forward and McGoldrick’s curler was kept out by De Vries, Murphy volleying the rebound into the sidenetting.
Trotter’s volley from Daniel Pinillos’ cross hit Berra and was cleared as a goal looked far more likely to come than in the opening half, Skuse then doing brilliantly to tip the ball away from Oliveira as he looked to pounce 10 yards out.
The intervention came at a price, Skuse picking up an injury with Jonathan Douglas his replacement.
Mendes exploded a right foot effort over after linking up with David Vaughan before Blues got the breakthrough on 75 minutes, Parr’s excellent right foot finish nestling high in the corner of the net.
Town threatened a second soon after, Sears’ shot deflected behind after Murphy played him in, then McGoldrick fired well over from a good position.
Murphy flashed a shot just wide as Town looked to extend the lead but Parr’s goal looked enough to give Blues the points until Trotter had the final word.