The Gingerbreads registered their first league win since September 1 to cause an upset for promotion chasers Witton Albion.
Evo-Stik Northern Premier League
Witton Albion 0
Grantham Town 2
Grantham took the lead in the 32nd minute when Paul Grimes struck from the penalty spot.
Both sides struck the post before Karl Demidh finally sealed the win with a second goal in injury time.