A last-gasp header from Matt Rhead was enough to earn Mansfield maximum points and deny Forest Green the chance to climb to second in the Blue Square Bet Premier.
With Wrexham losing at home to Lincoln, Rovers could have overtaken their rivals at the top end of the table, but they struggled to break down their opponents and went home empty-handed.
The visitors enjoyed the better share of possession in the early stages and came close to taking the lead after 10 minutes when James Norwood had a 12-yard effort blocked by Ritchie Sutton.
Rovers continued to knock on the door but were unable to cause Mansfield goalkeeper Liam Mitchell too many problems.
Mansfield had their fair share of chances and, in the 89th minute, Rhead rose highest to head the ball home and snatch his side all three points.