Peterborough United chalked up a deserved third win a row, as they ended MK Dons five game unbeaten run.
Goals from Peter Gain, Gavin Strachan, Craig Mackail-Smith and Richard Butcher fired big-spending Posh to victory, despite having defender Shane Blackett dismissed for a slap on Aaron Wilbraham.
Illness to Dean Lewington meant a change-round in the Dons starting line-up. Lloyd Dyer reverted to left-back, a position he frequented on-loan at QPR last season, Jon-Paul McGovern ahead of him, Jamie Smith pushed up to right midfield and Drissa Diallo coming in at right back.
As expected, Peterborough were unchanged for the third game in a row, with big-money strikers George Boyd and Craig Mackail-Smith the pair charged with beating the returning Lee Harper in the Dons goal. Former Don Craig Morgan took up his spot on the right of a three-man defence.
Posh started the brighter on a tight, bobbly pitch and Dons' concentration had to be spot on to avoid going behind. But there was little they could have done had Mackail-Smith's well-executed bicycle kick found the net rather than the foot of the post on three minutes.
The warning signs were there for the Dons when Mackail-Smith ran through on to Ben Futcher's pass and forced an excellent save from Harper, but from the striker's next involvement, Posh took the lead.
Running at the Dons defence, Mackail-Smith was fouled by Keith Andrews but a good advantage from referee Dean Whitestone allowed Boyd to shoot from the right. His shot was well saved by Harper but Gain followed up to do the rest from six yards.
Having lost Smith before the goal, Jude Stirling's introduction took the reigns off Dyer and the Dons started to cause a few problems. Twice Izale McLeod got at Morgan only to see his efforts blocked and Dyer made a useful break down the same flank.
But just as Allen's side were finding some rhythm, Posh hit them with a killer second. Adam Newton's deep cross was only partially cleared by Diallo and Sean O'Hanlon, the ball falling nicely for Strachan to rifle into the roof of the net from 12 yards.
Half-time saw the introduction of Leon Knight as the Dons went for broke, and within minutes he had leapt high above the Posh defence only to miscue his header.
Posh looked happy to play on the break and as Allen's side pushed on, McLeod went close when his left-foot shot was pushed round the post by 'keeper Mark Tyler.
The breaks were always likely to come and the first was a four-on-two the Dons did well to survive as Andrews and O'Hanlon forced Mackail-Smith wide and his shot flew over.
With the game seemingly in their control, Peterborough gave the Dons a lifeline when Blackett completely lost control with 20 minutes to play. With no apparent provocation, the Posh defender slapped Aaron Wilbraham right under Mr Whitestone's nose and it was no surprise when a red card was brandished.
It gave the Dons a lift and Platt's turn and deflected shot from the edge of the box nearly got them one back but for a full-stretch save from Tyler.
But Mackail-Smith put the game beyond doubt on 80 minutes. With the Dons short-handed in defence, the Posh striker was able to nip inside O'Hanlon before firing in a shot that squirmed under Lee Harper, despite his best attempts to keep it out.
That ended any hopes of a comeback, and when Butcher raced clear to make to four, it only served to rub salt in the wounds for the 1174 Dons that had followed their team up the A1 to see it.
It was a day to forget, summed up by substiture Jonny Hayes at the end, who shook his head in disbelief as his curling shot from the edge of the box bounced off both posts to safety.
