WATCH: MK Dons go 11 without at win at Stadium MK
Dons looked in total control of the game, with first Kieran Agard and then Dean Lewington coming close, before the Dons captain handled in the area to allow Vale their first opening 10 minutes before the break.
Lewington's handball appeared to be appeased when David Martin saved Alex Jones' penalty, but the rebound fell nicely for the Vale striker, who tapped into the empty net.
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Hide AdDons huffed and puffed in the second half but were restricted to half-chances, though Ben Reeves thumped the bar in stoppage time.
The result, Dons' fifth defeat of the season, leaves them 12th in the table.READ MORE: REPORT: MK Dons 0-1 Port ValeREAD MORE: Robbo's 'there to be shot at' after Vale defeat