A classy finish from Jermaine Darlington gave Wimbledon only their third home league win of the season.
Derby, who secured their First Division status with a 2-0 win over Millwall last weekend, looked sluggish in a one-sided first half, and Darlington's classy back-heeled finish was just reward for the Dons' dominance in the first 45 minutes at the National Hockey Stadium.
However Derby fought their way back into the game after the interval, and Wimbledon had goalkeeper Scott Bevan to thank for making a string of fine saves.
The visitors came desperately close to taking the lead early on, when Paul Peschisolido delivered a superb cross and Junior's header from the right edge of the six-yard box forced Bevan into a smart save.
The hosts responded with a decent opening of their own, but following Gary Smith's outswinging corner from the right, Dean Lewington failed to trouble goalkeeper Lee Grant, and sent his near-post header from six yards just over the crossbar.
The chance gave the Dons confidence and Malvin Kamara fired a left-footed effort from the right channel just wide of the left-hand post from the edge of the penalty area, and then Kamara forced Grant to produce a flying save to keep out his right-footed drive from 20 yards.
Wade Small then tested Grant with a right-footed strike, and Derby's Adam Bolder had to be alert to knock away Wayne Gray's goalbound header from six yards following Smith's corner.
The home side eventually got the opening goal their dominance deserved on 25 minutes, when Small delivered a low cross from the right flank and Darlington scored with a cheeky right-footed back-heel from six yards for his first goal of the season.
The Dons could have doubled their lead moments later, but Mark Williams fired a right-footed effort straight at Grant from point-blank range.
At the other end Derby wasted a rare opportunity when Junior curled a left-footed free-kick wide of the right-hand post from 30 yards.
Derby carved out the first opening of the second half when Ian Taylor drilled a right-footed shot from 20 yards, but Bevan did well to hold onto the ball. Moments later Taylor again tried his luck with a right-footed shot from the edge of the area following Tom Huddlestone's cross but Bevan was well positioned to gather.
Bevan was once again called into action to deny Junior's left-footed effort from the edge of the area and then the Dons stopper tipped over Marco Reich's speculative 30-yard effort as Derby continued to battle back into the match.
Reich and Junior again tested Bevan from distance but then Wimbledon came close with three chances in the space of two minutes, with Mark Williams, Harry Ntimban-Zeh and Small all spurning good opportunities.
Bevan thwarted Marcus Tudgay with a fine save late on and the Dons held on for their fist home win since November 1.
Teams
Wimbledon Bevan, Oyedele, Lewington, Williams, Ntimban-Zeh,
Kamara (Holdsworth 87), Darlington, Chorley,
Smith (Harding 45), Gray, Small.
Subs Not Used: Hawkins, Martin, Puncheon.
Goals: Darlington 25.
Derby Grant, Huddlestone, Kenna, Mawene, Johnson, Tudgay,
Reich, Taylor, Bolder, Junior (Costa 85), Peschisolido.
Subs Not Used: Oakes, Mills, Manel, Holmes.
Booked: Taylor, Junior, Reich.
Att: 6,509
Ref: P Crossley (Kent).