First-half goals from Lauren Brogan and Evie Carter cancelled out Elisha Whittaker’s free-kick for the visitors.
After a tense finale, Chesterfield managed to hold out and leave the title within touching distance with just one game remaining.
Manager Pete Jarvis was full of praise for his side’s resilience and fight after Mansfield continued to press for an equaliser right to the end of the match.
Jarvis said: “It felt like a really long second half, especially with the injury time at the end, but we have managed to withstand everything they threw at us.
“That was an incredible game of football, and to get this one over the line feels really good.”
Both sides were evenly matched in the reverse fixture back in November, and the game started in a similar fashion in the opening stages.
Mansfield looked to threaten with an early counterattack, but Amy Nowell thwarted it with a typically robust challenge.
Chesterfield responded by putting the ball in the back of the net moments later, only for the flag to be raised and Chloe Foster’s celebrations to be cut short.
It wasn’t long, however, until the net was rippling once more, and this time it did stand.
Alex Harding’s cross found Brogan in the centre of the box, who swivelled and volleyed home to give the hosts a 9th-minute lead.
Mansfield didn’t falter despite conceding and responded six minutes later.
After a controversial handball decision just outside the area, Whittaker stepped up and curled an inch-perfect free-kick into the top left corner.
The momentum seemed to shift in favour of the visitors after the goal as Mansfield pressed for a second.
But on the half-hour mark, Carter rolled home to calm the Chesterfield nerves.
Carter gambled on a long ball into the area and managed to beat the goalkeeper and poke it goalwards, which the onrushing Jess Waplington unselfishly let skid over the line.
After the break, the Spireites continued to look the more likely to score, with Carter and Waplington constantly looking to break beyond the Mansfield line.
A third goal wasn’t forthcoming as the half drew on and the Stags started to increase the pressure as they searched for an equaliser.
With 15 minutes to play, Paige Johnson was called into action as she produced a fantastic stop at point-blank range to keep out Olivia Standeven’s header.
From the resulting corner, more last-ditch defending was needed as Laura Porritt intervened with an outstanding goal-line clearance.
It was end-to-end stuff as Carter crashed an effort into the bar, and Foster’s acrobatic follow-up was also kept out.
As the game ticked into added time, it was Porritt who again came to the rescue with another crucial intervention on the line, again from a Mansfield set piece.
And with that, there was a collective sigh of relief around the ground as the referee called time on the game.
The result leaves the Spireites knowing that a win from their final league game would secure the title and promotion to the fourth tier.
The final game against SJR Worksop will be played at the SMH Group Stadium on April 12, with tickets on sale: https://www.eticketing.co.uk/chesterfieldfc
