Chesterfield 0-1 Mansfield
Calvin Andrew's first Mansfield goal was enough to earn a win at previously unbeaten leaders Chesterfield.
The Spireites were on top early on but wasted several chances, while Stags keeper Alan Marriott also saved well from Eoin Doyle and Jimmy Ryan.
Mansfield took the lead when Andrew headed in Ben Hutchinson's fine corner.
The hosts, who had Gary Roberts sent off late on, continued to dominate a feisty game but the Stags held on to stretch their unbeaten run to eight.
A spiky local derby, played in front of a crowd of 10,015, threatened to boil over towards the end of the second period as Chesterfield piled forward in search of an equaliser.
Hutchinson did almost add to the visitors' lead just before the interval when his shot struck the post.
But the woodwork also saved Mansfield when Sam Morsy's effort hit the bar and the home side were on top for long spells.
Marriott made numerous fine saves to deny Doyle, Roberts and substitute Armand Gnanduillet.
However, the Spireites, who had won seven and drawn one of their previous eight League Two games, were unable to find the breakthrough.
And their miserable afternoon was completed in the fifth of nine minutes of injury time when Roberts was sent off for violent conduct.
The Stags, who have won five of their last eight league games, move up to third in the table.
VIEWS FROM THE DRESSING ROOM
Chesterfield manager Paul Cook tells BBC Radio Sheffield:
"When any team loses on a Saturday and you've worked hard all week, you're always disappointed, but we've had a lot of plaudits lately and a lot of people have spoken about us really well.
"We've all been winners lately. Unfortunately today it hasn't gone our way and we must show some manners and class.
"Mansfield have come and beaten us in a local derby and we must give them a pat on the back and say 'well done'."