Dave Penney's side will have felt hard done by after seeing Ian Breckin head Forest into the lead in first-half stoppage time, after an opening 45 minutes that the visitors had dominated.
But, after the break - perhaps lifted by their ill-deserved advantage - Forest turned on the style and romped to victory.
A header from John Thompson and a Nicky Southall cross that flew directly into the top corner, put Forest 3-0 up by the 53rd minute, before Gareth Taylor capped things off with a spectacular volley in the 67th minute.
Having disposed of Aston Villa and Manchester City in the Carling Cup - and given Arsenal an almighty scare - Doncaster are not a side known to flinch when faced with a supposedly bigger club.
And, for half-an-hour at the City Ground, it was hard to tell which was the club that once graced the Premiership and which was the side from South Yorkshire with a more modest history in the lower leagues of English football.
Penney has installed a strong sense of belief in his hard-working Doncaster side - and they were undaunted by Forest's proud home record, that had seen them win eight previous matches on the banks of the River Trent.
Come half-time, their primary emotion will have been one of injustice, after dominating for long periods, only to see Breckin snatch a headed goal deep into injury time for a Forest side that had provided little in the way of attacking endeavour.
Prior to that, it had taken Gary Megson's side 25 minutes to register even a single effort on goal, as Doncaster went after Forest with some entertaining, flowing football.
Only a goal-line clearance from Nicky Eaden had spared Forest's blushes prior to that, after Jonathon Forte had carried the ball around the advancing Paul Gerrard, before firing a shot towards the exposed net that the full-back did well to block.
Paul Heffernan also went close to giving the visitors the lead, with a neat turn and shot from the edge of the box that flashed only inches wide of Gerrard's post.
Nicky Fenton, the other former Notts County player in Doncaster's line-up, was also unlucky not to find the back of the net, as he hammered a powerful drive from 20 yards that dipped only narrowly wide.
Forest had taken 25 minutes to register even a single effort on goal with Kris Commons striking a shot that was always rising over the bar.
After the interval, the story could not have been more different. It took only five minutes before another Southall corner had the same effect, with Thompson bundling the ball home from close range, although the Doncaster players claimed the ball had not crossed the line.
And, three minutes after that, it was 3-0, with Southall again the instigator, as he swung in a cross from the Forest left that deceived everyone, as it looped over keeper Jan Budtz and into the back of the net.
Taylor then capped things off with a fine right-foot drive, after Nathan Tyson had turned provider.