A brace from Adam Cunnington boosted Tamworth's survival bid and put a major dent in Forest Green's play-off hopes.
The striker took his tally for the season to 20, sliding in at the back post to poke in before heading home a Lee Hendrie cross from close range.
Rovers pulled one back as midfielder Yan Klukowski tucked home from six yards after good work by James Norwood.
Tamworth held firm and moved three points clear of the drop zone, with Rovers eight points off the play-offs.
VIEW FROM THE DRESSING ROOM
Forest Green Rovers manager Dave Hockaday told BBC Radio Gloucestershire:
"They wanted it more than us. We got bullied in the first half and that can't be.
"It doesn't matter how big you are - nobody bullies me. I'm really angry at them at the moment,
"My players need to have a look at themselves because that's not good enough and however long it takes, we'll get promoted and get to the promised land.
"They'll be back in tomorrow morning. One way or another we'll sort it out because this is a full-time job and that wasn't good enough."