George Burley described this game as a six-pointer and Stuart Murdoch watched with growing anger as his players gift wrapped the spoils.
Wimbledon were their own worst enemies and remain deep in relegation trouble after Derby rescued a win from a game that looked to be slipping away from them.
Although an own goal from Nico Herzig had given the home side an early lead, Wimbledon skipper Nigel Reo-Coker quickly cancelled that out as the visitors took control.
But they failed to cash in and fell apart at the start of the second half to give Derby a vital win.
Two goals in the space of 60 seconds floored the visitors and left Murdoch to admit "it was an unacceptable performance from professional players".
Derby manager George Burley was relieved, and said: "It was so important to get this win, it was a six-pointer and this gives us a little bit of breathing space." But Derby will need to play much better if they are to pull themselves away from the relegation zone and will find few teams as generous as Wimbledon.
Herzig dived to head a cross into his own net in the 13th minute and the young German defender also deflected a shot past Steve Banks in the second half.
In between Wimbledon had played the better football and Reo-Coker finished sweetly in the 20th minute when Adam Nowland sliced open Derby's defence.
Wimbledon should have gone in front on the half hour when Wade Small squared the ball to set up Patrick Agyemang, but the striker put a shot wide from an inviting position.
Small was denied by a flying save from Grant four minutes later and Wimbledon were well placed to go on and win the game, but collapsed after the interval.
Marcus Tudgay scored his first senior goal when he drove a shot against Herzig in the 52nd minute and the game was sealed a minute later when Candido Costa crossed from the right and Lee Holmes slid in at the back post to push the ball over the line.
Derby could have had more goals as Wimbledon slid to another defeat that leaves them dangerously adrift at the bottom of Division One.