It was a deserved victory for a Forest side, who extended their unbeaten run under Frank Barlow and Ian McParland to six matches, maintaining their faint hopes of making the play-offs in League One. But it owed much to the defensive frailty of the Dons, who face a desperate fight to avoid relegation.
They played much of the second half with only ten men after Dean Lewington was sent off as he picked up a second yellow card, for a foul on Nathan Tyson, in the 54th minute.
But the damage had already been done by that stage, following a 19th minute Trent McLenahan own goal and a slip from goalkeeper Ricardo Batista in the 34th minute, which allowed Grant Holt to make it 2-0. Skipper Ian Breckin rounded off the scoring with an injury time header for Forest.
Grant Holt had enjoyed the best of a sparse number of chances in the opening exchanges, but headed wide of the target after Kris Commons had picked him out with a pin-point cross from the left.
But, while Forest had started poorly by their standards, MK Dons had looked shaky at the back right from the off and it was no surprise when a moment of sloppy defending cost them dear.
This time it was John Curtis who swung in a dangerous ball from the right side, after a neat build up involving Tyson and Sammy Clingan and, under no pressure, Dons defender McLenahan dived to plant a header into the back of his own net from close range.
The goal sparked Forest into life and it was no surprise when they doubled their advantage, following a period of pressure. Although, when it came, the goal again owed a great deal too some poor defending.
This time it was pitch-length punt from Curtis which the Dons defence left to bounce through to keeper Ricardo Batista, but the Portuguese stopper dropped the ball under pressure from Holt, who was left with the simple task of stroking the ball into an empty net.
Forest continued to pressure, but without ever really finding top gear, with Commons twice coming close with long range efforts. The visitors' biggest threat came through former Forest man Gareth Edds, who fired a close-range effort into the side netting.
The second half began with another defensive disaster for the visitors as Lewington, who had been booked for dissent following the second Forest goal, found himself sent off after bringing down Tyson to earn himself a second yellow card.
Commons should soon have made it 3-0, after being put in down the left by Gary Holt. The winger beat two defenders before firing a shot straight down the throat of Batista from ten yards.
Grant Holt also came close with a curling effort which flew into the side netting, while Tyson was denied by a fine save from Batista, after connecting sweetly with a half volley from ten yards.
But it was not until the 93rd minute that Forest made their domination tell, as Breckin headed home a Commons corner to make it 3-0.