The Dons’ survival hopes were dealt a big blow after falling to a 4-0 defeat at the hands of Rotherham United.
The Dons made the worst possible start, falling behind in the opening minute when Derbyshire turned home at the second attempt after Grant Ward had raced down the right and crossed.
Karl Robinson’s men responded with a shot from Alex Revell and a header from Dean Bowditch – the former was saved by Lee Camp and the latter went wide of the target.
Camp was again called into action shortly afterwards to gather a dangerous Josh Murphy cross, this coming prior to Bowditch seeing a delivery cut-out after a nice exchange with Revell.
However, it was Rotherham who extended their lead on 17 minutes when Best sent Cody Cropper the wrong way from the spot after the USA U23 international was adjudged to have fouled Richard Wood.
Cropper ensured the score remained at 2-0 just past the halfway point of the first half, diving at the feet of Derbyshire after the Millers had delivered a ball from the right.
At the other end, the Dons enjoyed a good spell of pressure around the 30-minute mark, which included a cross deflecting on to Camp’s crossbar.
Revell then turned a Murphy cross not too far past the post as the Dons continued to look for a way back into the game, but they went in trailing by two at the break.
The men from MK1 started the second half on the front foot and Dean Lewington curled an effort just over the top from Jake Forster-Caskey’s corner.
But the visitors made it 3-0 on 54 minutes when Broadfoot powered Joe Newell’s right-wing free-kick into the back of the net, despite the best efforts and fingertips of Cropper.
Carl Baker and Samir Carruthers were introduced as the Dons looked for a response, but it was one of the starters – Forster-Caskey that came closest to pulling one back when he forced Camp into a fine save from a 25-yard free-kick.
The Brighton & Hove Albion loanee then went even closer on 71 minutes, sending a fierce 25-yard effort goalwards which came crashing back off the crossbar with Camp beaten.
Rotherham made it 4-0 on 80 minutes when Smallwood picked the ball up and sent a dipping volley past Cropper from 25 yards.
Revell almost scored a consolation with just over five minutes remaining but he couldn’t keep his header down.
MK Dons: Cropper; Baldock, Kay (Maynard 77), Walsh, Lewington (c); Potter, Forster-Caskey; Bowditch (Baker 67), Williams (Carruthers 67), Murphy; Revell.
Unused subs: Burns, Spence, Long, Powell.