The Stags remained firmly in relegation trouble after their fourth successive away defeat, despite fighting back from conceding two early goals to poor defending.
Paul Mullins and Kevin Ellison pounced before Simon Heslop quickly replied with a delightful curling free kick.
But the Stags rarely looked like equalising and were indebted to fine first half saves from Lenny Pidgeley for keeping them in contention.
Teenager Joe Fitzpatrick made his debut as a half-time substitute in a reshaped midfield that was shorn of Chris Clements before the match, another injury victim.