Matt Green put the Stags in front with a close-range header from Mal Benning's inviting free-kick and took his tally for the season to 14 with a second four minutes later, getting a glancing touch on Chris Clements' deep free-kick.
Mansfield had Jamie McGuire sent off just before half-time for a late challenge on Brendan Moloney - his second yellow card - and it proved costly.
Ricky Holmes pulled a goal back from the penalty spot and it was all square after 68 minutes when John Marquis scored from close range.
AFC Wimbledon beat Plymouth to secure League One promotion
Second-placed Oxford remain 13 points behind after they were held to a goalless draw at Cambridge.
Plymouth moved into the automatic promotion places as they held off a spirited comeback from relegation-threatened York to claim a 3-2 win.
Argyle took the lead after 21 minutes when Gary Sawyer's cross was knocked down into the path of Jamille Matt and he converted from close range.
The Greens doubled their advantage from the penalty spot in the 31st minute after Dave Winfield had brought down Matt. Reuben Reid stepped up to slot home.
It was 3-0 before the break when a Graham Carey free-kick was thumped past his own goalkeeper by the head of York defender William Boyle.
Players from both teams surround Referee Darren Handley.
Image credit: Eurosport
Russell Penn pulled a goal back for York after 52 minutes and they made it 3-2 from Luke Summerfield's penalty with four minutes remaining, but the visitors could not find an equaliser.
Accrington moved up to fourth following their 2-0 win at Newport.
Billy Kee took his tally for the season to 17 to put Stanley in front and they added a second two minutes later when Josh Windass converted Piero Mingoia's cross.
Bristol Rovers' six-game winning run came to end in a 3-2 defeat at Carlisle which saw them drop to fifth.
Jack Stacey curled in the opening goal for Carlisle in the 11th minute, b ut Rovers were level after 27 minutes when Matty Taylor took advantage of a mix-up in defence to hook in an equaliser.
The Cumbrians regained the lead when Charlie Wyke poked home at full stretch, but again the Pirates hit back as Taylor squeezed in his ninth goal in seven matches.
Carlisle took the lead for the third time with five minutes remaining as Jason Kennedy chipped the goalkeeper and this time they held on.
Notts County's clash with Wycombe had been under threat before kick-off with the Meadow Lane pitch waterlogged. The game went ahead, but neither side could find a goal.
At the bottom, Hartlepool were the big movers as a 2-0 win at Leyton Orient saw them jump from 21st to 17th.
Billy Paynter fired the visitors ahead early in the second half as he slid in at the back post.
And Nathan Thomas doubled Pools' lead with a superb solo effort in the 69th minute, nutmegging a defender before lashing the ball into the roof of the net.
Elsewhere, goals from Jake Taylor and Ollie Watkins earned Exeter a 2-0 win at Crawley and John Akinde's penalty in time added on snatched Barnet a 2-1 win at home to Luton.
Luke Gambin had put the Bees ahead, but Cameron McGeehan equalised five minutes from time.
Penalty levels League Two play-off first leg between Portsmouth and Plymouth Argyle
Oxford and Bristol Rovers grab promotion as Accrington Stanley blow it