Jordan Rhodes' 39th goal of the season helped inspire Huddersfield to a commanding away victory.
The prolific marksman glanced home a 32nd-minute cross from 17-goal strike partner Lee Novak, who wasted a glorious second-half chance to double the visitors' advantage at Stadium:MK.
But Jack Hunt's well-taken finish ensured Town took firm control of the tie ahead of Tuesday's second leg at the Galpharm Stadium, and left the Terriers dreaming of Wembley success in what is their third successive attempt at play-off glory.
It was a woeful afternoon for a lacklustre Dons, who were embarking on their third play-off campaign in four years as they bid to make the second tier for the first time since their change of identity in 2004.
However they were spared the boos from home supporters which dominated the headlines following their final-day defeat to Walsall.
Rhodes, with 38 goals in 42 appearances prior to today, was recalled to Town's XI having been rested for the last two games, while the Dons also showed one change as centre-back Gary MacKenzie returned.
The hosts were first to threaten as former Leeds, Manchester United and Newcastle midfielder Alan Smith fired off target after seven minutes.
Calum Woods drilled wide for the Terriers amid a lively but largely poor quality opening quarter with little to do for respective goalkeepers Ian Bennett and David Martin.
But all that changed in the 32nd minute.
Martin made a great parried save to deny impressive substitute Kallum Higginbotham but the ball was recycled to Novak on the left and his lofted cross was nodded home by Rhodes.
Smith sent a good opening into the side-netting at the other end as the goal sparked brief life into the hosts but it was a below par opening 45 minutes from Karl Robinson's side.
Bennett had to make save to deny Dons skipper Dean Lewington within 35 seconds of the restart.
It was an improved opening by the home side but it did not last long and Novak, with three goals in his last three games, blew a great chance to put Huddersfield two nil ahead as he fired wide when clean through.
But Hunt soon ensured Town did stretch their lead in the 73rd minute, exchanging some great play with Higginbotham before sending a superb finish past Martin from the edge of the penalty area.
Terriers skipper Peter Clarke emerged unscathed after a nasty-looking challenge which provided seven minutes of injury time.
Yet, despite Jabo Ibehre's late header which Bennett saved, the visitors comfortably saw out proceedings to leave them firmly in pole position for a showdown with either Sheffield United or Stevenage on May 26.