Ched Evans got the winner as Sheffield United beat Chesterfield to keep their neighbours bottom of the table.
With eight minutes remaining, the Welsh striker picked the ball up 30 yards from goal, beat two defenders and fired home from 15 yards out.
The struggling Spireites had hit the crossbar in the 62nd minute from Leon Clarke's overhead kick.
Blades' Stephen Quinn, who had a strike ruled out for offside, forced a good injury-time save from Greg Fleming.
Veteran Chesterfield striker Jack Lester came off the bench late on after more than two months on the sidelines with a broken arm but he could not find a leveller.
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Chesterfield manager John Sheridan told BBC Radio Sheffield:
"Obviously result-wise I'm very disappointed but I thought we were really in the game and I'm gutted that we haven't ended up getting anything out of the game.
"They are a good team. I think they will definitely be up there at the end of the season.
"I think we matched them in lots of departments and for the majority of the game and it just really hurts that we haven't got anything."
Sheffield United boss Danny Wilson told BBC Radio Sheffield:
"I think the last few weeks we've been talking about tightening up at the back and in certain areas, and we've been given rewards with that.
"I think the performance today was very, very strong again and it had to be.
"John and Chesterfield put out a very strong side against us today and they made it very difficult, very physical at times.
"From our part in it, there were pockets where we could have done better with the situations that developed, but a fantastic moment of inspiration from Ched and it separates the two teams but it was a typical hard-fought derby game."