Jemal Johnson fired MK Dons in front in the 17th minute with a wonder strike, cutting in from the right and unleashing a left-foot piledriver from 30 yards.
The Dons doubled their lead two minutes before the interval when Johnson’s left wing cross was drilled in from close range by Wilbraham after the Robins’ defence failed to clear.
Wilbraham grabbed his 10th goal of the season with the simplest of tap-ins in first half stoppage time after Luke Chadwick’s cut back and grabbed his hat-trick in the 58th minute following a break by Jason Puncheon.
Spencer pulled a goal back from close range before Johnson scored the Dons fifth after he had run the length of the pitch.
Spencer then swept in a Nicholas Bignall cross to make it 5-2 before converting an 81st minute penalty. The big striker was then dismissed for a foul on Dean Lewington.