Colin Calderwood's team looked likely to hold on for a valuable victory, following a first-half strike from Junior Agogo.
But referee Gary Sutton pointed to the spot after Wes Hoolahan had gone down in the box under Wes Morgan's challenge.
Forest were furious with the decision - but Hoolahan kept his head to fire home from the spot at the second attempt, after being ordered to retake his first successful penalty and earn Blackpool a share of the spoils in the 90th minute.
Frustrated Forest supporters booed their players off the pitch, after again seeing them drop points late in the game.
After being given a tough reception by the home fans in their last City Ground outing, when Northampton had provided stubborn opposition, Forest were in need of a bright start.
And though the damp conditions made life difficult for both sides, Forest got exactly the kind of beginning they had hoped for, as they took the lead in simple fashion in the 16th minute.
When Paul Smith had parried a fierce shot from Blackpool's David Fox, punching well clear of his box, Forest launched into a swift counter which saw Michael Jackson lose his footing and allow Agogo a clear run on goal.
The striker kept his composure as Rhys Evans raced off his line and slotted a simple finish under the keeper's body and into the centre of goal.
At the other end Smith was less convincing, making hard work of a straightforward drive from Ian Evatt, from 20 yards, which he only succeeded in pushing into the danger zone on the edge of the six-yard-box where Ian Breckin, fortunately, was on hand to clear.
At this point it was the visitors who looked dangerous as Hoolahan was harshly booked for diving in the box when it appeared he had been felled by a desperate lunge from David Prutton, before Scott Vernon directed a good headed chance straight into the arms of Smith.
But Forest finished the half with a late flurry of their own, with Agogo hitting the bar with a spectacular 35-yard volley that had keeper Evans well beaten.
Blackpool continued to play with ambition and were almost rewarded as Fox lashed a shot narrowly wide, while the City Ground crowd urged Forest to up their own tempo.
They responded with a neat move - but a poor finishing effort from Grant Holt - and a Prutton effort that had Evans scrambling to make an impressive save.
Smith had to save twice in spectacular fashion, firstly to block Keigan Parker's driven effort towards the near post and then to palm a powerful close-range header from Evatt wide.
But he could do little when referee Sutton awarded a harsh looking late spot-kick, following Morgan's tackle on Hoolahan - which the winger duly got to his feet to convert.