Matt Rhead's late header gave Mansfield a first win in five games against Forest Green at Field Mill.
Kieron Forbes and Matt Taylor fired wide of Liam Mitchell's goal as Rovers dominated a quiet first half.
Taylor also went close after the break when Mitchell saved his downward header from Jared Hodgkiss' fine cross.
Rhead had earlier fired wide from distance, but a header from Exodus Geohaghon's long-throw consigned Rovers to a third successive defeat.
With Wrexham losing at home to Lincoln, Rovers could have overtaken the Welsh outfit and climbed to second in the table but they struggled to break down the Stags and went home empty-handed.
VIEW FROM THE DRESSING ROOM
Mansfield Town manager Paul Cox told BBC Radio Nottingham:
"I don't think anyone could say we didn't deserve it today. I thought they boys worked extremely hard and we did create some great chances.
"I am over the moon but it is only one win and this could be a base for us to start from.
"We looked structured, we looked organised and more importantly we looked hungry, which is the main ingredient for success."
Forest Green Rovers manager Dave Hockaday told BBC Radio Gloucestershire:
"We feel like we've run over a black cat or smashed some mirrors or something. It feels like things just aren't quite going for us.
"We've had the best chances in open play and we haven't taken them.
"We defended brilliantly and had to make a few changes really late on. They've given me everything and I can ask for more.
"We've been punished late again, we've got to take that on the chin and we've got to learn."