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'."
Chesterfield 01 Lee 04 Hird 06 Cooper Booked 15 Humphreys 25 Talbot (Devitt - 87' ) 05 Morsy Booked 07 Darikwa (Gnanduillet - 55' ) 10 O'Shea (McSheffrey - 55' ) 11 Roberts Dismissed 12 Ryan 17 Doyle Substitutes 20 Chapman 08 Togwell 23 Evatt 27 Edwards 16 Devitt 21 Gnanduillet 28 McSheffrey Mansfield Town 01 Marriott 02 Sutton 04 Dempster 12 Tafazolli Booked 13 Howell 16 Jennings Booked 17 Beevers 18 Hutchinson (Meikle - 63' ) 23 McGuire Booked (Daniel - 78' ) 11 Clucas (Rhead - 81' ) 24 Andrew Substitutes 08 Murtagh 30 Daniel 09 Rhead 10 Stevenson 14 Speight 20 Meikle 36 Palmer
Ref: Robert Madley