Two second-half goals in four minutes from Michael Boulding sent County sliding to their fourth successive defeat as Mansfield defended resolutely to keep their first clean sheet for 20 games.
And Boulding almost completed a memorable treble, but his diving header from a Dan Martin cross flew narrowly wide.
Stags, unchanged for only the second time this season, welcomed back Gareth Jelleyman to the substitutes' bench after a month-long injury lay-off.
New County boss McParland made two changes – Paul Mayo back from suspension to replace broken foot victim Crow and Andy Parkinson in for Somner – and also switched the formation from 4-3-3 to 4-4-2.
A fine block by former County player Dan Martin denied the visitors an early goal. Lawrie Dudfield brushed off Alex John-Baptiste and when the wingman's cross from the left finally fell to Richard Butcher, his fierce drive was turned away by the full back.
County dominated the opening minutes, looking more like the home side in a local derby, and Spencer Weir-Daley's shot on the turn almost found the breakthrough.
It took the Stags 10 minutes to pose a threat, but from their first chance the home side should have scored. Boulding's flick released Stephen Dawson and his pass found Nathan Arnold clear inside the penalty area, but the youngster's shot was beaten away by former Stags' star Kevin Pilkington.
The keeper then reacted quickest, to race out and take the ball off the boot of Simon Brown as the striker threatened to capitalise on Lee Bell's knockdown.
The Stags, in front of the biggest home crowd of the season, again went close in the 32nd minute with John Mullins' header from a Matt Hamshaw corner cleared off the line by Gary Silk.
County weathered the mini storm and roared back as an attacking threat themselves. First Dudfield's volley was charged down by Jake Buxton, before Parkinson's follow-up flashed into the side-netting.
Then from a short corner Neil Mackenzie's cross was headed over by the unmarked Stephen Hunt.
A minute into the second half Bell's curling free-kick was well held by Pilkington, but there was no let-off in the 57th minute. Austin McCann held Hamshaw as he turned on the edge of the area and Boulding drilled the penalty home.
Four minutes later Brown lifted the ball over two defenders and Boulding waited patiently for the ball to drop before hammering in from 12 yards for his eighth goal of the season.
The striker almost grabbed a hat-trick when his diving header from Martin's cross flew inches wide and Arnold tested Pilkington from 20 yards as the Stags tried to secure victory with a third goal.
County rarely threatened a fight-back, although substitute Hector Sam scuffed a late close-range shot wide.