The hosts needed a win and they started in positive mood. Zac Corbett went close with a long-range effort and then on 18 minutes they went ahead.
A cross from Joel Senior was headed past Lambs` keeper Shaun Rowley by Jason Gilchrist.
Five minutes before the break, FC United `keeper Lloyd Allinson was forced to punch off the line from Aman Verma.
But the home side deserved their interval lead.
However, 7 minutes into the second half, Tamworth pulled back on level terms when a well-worked free-kick was converted by Connor Taylor.
FC United almost restored their lead on 63 minutes when a good turn and shot from Gilchrist was well saved by Rowley.
But 2 minutes later, Gilchrist wasn`t to be denied as he made it 2-1 with a cross-cum-shot that deceived Rowley.
The temperature on the pitch began to heat up and the referee was busy with five bookings in quick succession.
The hosts` Senior then hit a post with a free-kick and then 3 minutes from time, the Reds were awarded a penalty when Rowley made a hash of a clearance and kicked Steve Irwin instead of the ball and Irwin made him pay from the spot to confirm victory.