The striker’s 86th-minute penalty finally broke Rotherham’s resolve on an afternoon when manager Paul Warne’s side had set themselves up to frustrate and contain their hosts.
Their plan worked well with Forest only allowed rare sights of goal – right up until Ben Osborn had his heels clipped in the area by Ryan Williams.
Grabban, who scored 18 goals in 43 appearances for the Millers in 2011-12, was the coolest man in the City Ground as he netted from the spot to secure three hard-fought for points.
Defeat stretched Rotherham’s run without an away win at Championship level to 30 matches – a record reaching back to April 9, 2016.
Fourteen visits to Forest have also failed to produce a win, but Warne was far from dispirited.
He could have argued that Forest’s Adlene Guedioura was slightly fortunate not to collect a second yellow card for a foul on Williams early in the second half, but he refused to complain about that and admitted the penalty decision was probably the right call.
Instead he said: “I am proud of these players – that is my overall feeling.
“I am disappointed with a few things, as you always are when you have lost, but one mistake has cost us here. I think the goal was one of their few shots on target.
“I am not the sort of manager who comes out and blames the referee for results, that is pathetic.
“I think if you watch the highlights you can form your own opinion (over the Guedioura incident).
“There are turning points in games all the time and it was a big moment, but that is not why we have lost the game.
“I do not have any complaints about the penalty. I haven’t seen it back, but if it was down the other end would I want a penalty? Darn right I would.
“Overall the lads have given me everything. I am proud to be their manager. I feel sorry for them that they have come away with nothing because they deserved something.”
Nottingham Forest: Pantilimon, Janko, Hefele, Fox, Robinson, Guedioura (Lolley 60), Watson, Gil Dias (Cash 72), Joao Carvalho (Bridcutt 90), Osborn, Grabban. Unused substitutes: Steele, Goncalves, Dawson, Darikwa.
Rotherham United: Rodak, Jones, Ajayi, Wood, Mattock, Towell (Taylor 88), Vaulks, Manning (Palmer 72), Williams, Proctor (Smith 46), Vassell. Unused substitutes: Vyner, Forde, Price, Wiles.
Referee: R Jones (Merseyside).