The Red Devils are now six points clear of the League One drop zone, but the result surely ends the Dons’ hopes of reaching the play-offs.
Crawley made the perfect start as an excellent pass by Jamie Proctor found the unmarked Andy Drury and the midfielder kept his composure to score when one-on-one with the goalkeeper.
Izale McLeod should have equalised for MK Dons, but he wastefully lobbed over the crossbar after he had been picked out by Alan Smith.
A mistake by Jordan Spence gifted the Red Devils a second goal just before half-time as he missed Mark Connolly’s clearance with Proctor delaying before giving Mike Jones an open goal to finish.
Crawley goalkeeper Paul Jones made a brave save at the feet of Mark Randall early in the second half with Spence also firing a low shot wide for the deflated hosts.