It looked like Dons had ruined their chances after missing a series of easy opportunities but late strikes from Gary Smith and Izale McLeod mean things will go to the final game of the season.
The first half was all about the visitors who dominated from the start and could have been ahead in minutes. Clive Platt played in McLeod but against a narrowing angle he scuffed his shot straight at the keeper.
McLeod was then gifted another chance on 12 minutes when Albert Jarrett's pass put him clean through on goal. His precise lob looked to be going in but just drifted over.
Dons continued to dominate when Jermaine Easter did his side no good on 26 minutes by clattering into left-back Dean Lewington. The referee judged that he led with this elbow and he was shown a red card.
McLeod made it a hat-trick of misses when he expertly chested down and cut inside his man before blasting over from 10 yards, after he was picked out well with a cross-field pass from Keith Andrews.
Milton Keynes must have expected to push home their advantage and win the game easily in the second half but Wycombe came out rejuvenated.
They kept the Dons pegged in their own half and went close when Scott Golbourne's half-volley just went over.
Wycombe then had a great chance to take the lead when Matt Bloomfield squared well for veteran striker Tommy Mooney but Don's keeper Ademola Bankole charged him down well so he had nowhere to shoot.
It seemed like Dons would not get the breakthrough until substitute Gary Smith pounced after Sean O'Hanlon's shot had been saved and he blasted in from close range.
Then McLeod made up for his earlier misses when he skimmed his marker before tucking home with this left foot to seal the game.