Second best for virtually the whole of the 90 minutes, Rochdale turned the game on its head in time added on to snatch victory from the jaws of a deserved defeat.
The Dons completely bossed the first period as Rochdale looked leggy and out-of-sorts and Paul Ince's side deservedly took the lead on 15 minutes when the evergreen Kevin Gallen nodded an inviting Lloyd Dyer cross past the unprotected James Spencer.
Somehow Rochdale dragged themselves back into things courtesy of a brilliant individual goal by striker Chris Dagnall. The 21-year-old, who looked dangerous all game, appeared to have few options available to him as he took control of the ball outside the Dons penalty area. With no pass on, he looked up and curled a stunning 20-yarder into the roof of the net.
Within a minute Paul Ince's side were back in front as they passed the ball through an accommodating defence and left Gallen with a simple chance.
With Milton Keynes seemingly heading for victory Rochdale turned the game on its head.Rory Prendergast fed fellow substitute Adam Le Fondre and having been allowed to carry the ball forward he produced a similar shot to Dagnall that keeper Willy Gueret got to but could only palm into the net.
Still in stoppage time an excellent Prendergast cross was met by Le Fondre and after his effort rebounded off the cross-bar Dagnall reacted first to smash home for his second of the game and give his side an undeserved first victory of the season.