Two late goals broke ten-man Mansfield's hearts after they had held first division Derby at 1-1 for over an hour.
The Stags, reduced to ten men after just 90 seconds, managed to score their first goal in 372 minutes.
But late goals from Malcolm Christie and substitute Ian Evatt sent the Rams through and condemned the Stags to their fifth successive defeat - their third at home in 11 days.
In the 71st minute Christie slid in to convert Lee Morris' left-wing cross and then seven minutes later Evatt's close-range header from another Morris cross somehow got past keeper Kevin Pilkington.
Afterwards manager John Gregory said: "It was a good night for us. We created lots of gaps in their defence in the second half and it wouldn't have been an injustice if we had won 6-1."
County, like the Stags struggling in League football, named a strong side for the derby clash - but there was no place in the starting 16 for young midfielder Adam Murray, who was such a big hit in a loan spell at Field Mill at the end of last season.
The Stags, after leaking 23 goals in just seven games this season, switched to a five-man midfield and played with just one striker in a bid to shore up the worst defence in England this season.
Their uphill task became even harder after just 90 seconds when Derby-born captain Lee Williamson was sent off for a rash challenge on Adam Bolder, the midfielder red carded for showing his studs as he slid in.
Incredibly the Stags then struck first, Neil Moore hammering in Iyseden Christie's cross off the underside of the bar after County failed to clear Wayne Corden's eighth minute corner.
But within two minutes the first division side were level. Christie weaved his way to the left byline and his low cross was expertly finished at the near post by the unmarked Morris.
Chris Riggott and Branko Strupar went close to giving County the lead and then Christie sliced wide as the visitors began to make the extra man count.
Evatt twice went close as well, either side of half-time, and Christie and Bolder also saw shots flash past the post as Derby stepped up the pressure against the defiant ten men.
Substitute Georgi Kinkladze and Brian O'Neill then failed to find the breakthrough before Christie and Evatt struck to break home hearts