The home side had the majority of possession but ended up on the losing side after Junior Agogo scored for the third time in the space of five days.
Chesterfield, though, were furious that referee Mike Thorpe awarded a penalty when the big striker appeared to go down easily after side-stepping former Forest goalkeeper Barry Roche.
But even without that controversial incident, Chesterfield might still have enjoyed a better day if Colin Larkin had accepted two chances either side of Agogo's first goal.
Certainly, it was the home side who looked the sharper and hungrier in the first half when Paul Hall almost opened the scoring after a superb seventh minute run and a low left-foot shot that went just wide.
But the former Jamaica international should have scored when Peter Holmes got away on the left and crossed to the back post where Hall dragged a shot back across goal from only six yards.
Forest did find the net before the break after Roche had saved from Agogo, but the ball was fractionally out of play before it was played back for James Perch to score.
But the second half contained far more incident beginning in the 50th minute when Hall put Larkin in on the right but he pulled his shot wide of the far post.
Forest took the lead with a classic breakaway goal six minutes later when former Chesterfield defender Ian Breckin won the ball in his own area before passing to Jack Lester whose clever touch sent Agogo between the central defenders to beat Roche with a low right-foot shot from just inside the box.
The match erupted in controversy in the 62nd minute when a long ball from Kris Commons caught Chesterfield waiting for an offside flag that never came and Agogo went clear, but after going past Roche he went down and the referee pointed to the spot.
Roche was booked but was convinced he had made no contact with the striker and Agogo took the penalty himself and beat the keeper's dive low to his right.
But Chesterfield came fighting back and they got their reward five minutes later when Alex Bailey sent over a superb cross which Aaron Downes headed past Paul Smith's despairing dive.
Forest now had their backs to the wall and manager Colin Calderwood responded by making two defensive substitutions to try and stem the blue tide.
But the visitors should have killed the game off when Lester went round Roche but, with the goal at his mercy, Bailey got across to make a crucial block.
Forest had more anxious moments when Julian Bennett threw himself in the path of a goalbound volley from Larkin and David Prutton denied substitute Paul Shaw an equaliser in the third minute of stoppage time when he blocked another close-range strike.