A header from Arturo Lupoli in the third minute of stoppage time completed a memorable recovery by the home side who had trailed to a 39th minute goal from Ipswich winger Gary Roberts.
But Steve Howard headed his ninth goal of the season ten minutes into the second half, and then Lupoli won the game to shatter Ipswich's brave resistance when it looked as if the visitors had done enough to take a point.
Ipswich will look back on Derby's two goals and question the marking that allowed Howard and Lupoli the chance to keep Derby on the heels of the Championship's top two.
Howard was left unmarked to glance in a corner from Morten Bisgaard and Michael Johnson was also given too much room to set up Lupoli at the end.
There was little to suggest Derby would win the match in such dramatic fashion after both teams had stuttered through a tepid first half in which a goal from Roberts followed a controversial decision to deny Howard a 38th-minute header.
The striker's effort was ruled out for a push on Richard Naylor and Derby suffered a double blow when Roberts volleyed the ball into the bottom right-hand corner from 20 yards after Alan Lee had chipped the ball in.
But Derby have shown great spirit this season, and they bounced back again when Howard was given the opening to guide a header in off the post.
The visitors were reduced to ten men when Simon Walton was shown a second yellow card for a late tackle on Michael Johnson and Derby sensed the game was there to be won when Lupoli began to stretch the Ipswich defence.
Lewis Price made a stunning one-handed save to deny him in the 63rd minute and he was close to scoring 11 minutes later with a low shot that narrowly went wide.
But it looked as if Derby would be frustrated until they won a corner deep into stoppage time and Michael Johnson headed a ball down which bounced invitingly for Lupoli to head into the net.