Barnet snatch all three points thanks to Alex Nicholls' strike in the third minute of stoppage time.
It was an end-to-end affair at The Hive London. Barnet's first shot came through Ruben Bover 12 minutes in, but it was comfortable for Adam Collin.
Jonathan Forte was denied by an excellent last ditch tackle from Charlie Clough as the substitute raced down on Craig Ross' goal.
Alex Nicholls had a low snapshot saved and Forte shot inches wide of the right hand post.
Forte had another chance for the visitors after the restart, but Craig Ross pulled off a good save with his feet.
Home debutant Jordan Nicholson had a goalbound effort well saved by Collin, the ball fell to Simeon Akinola but he couldn't get a clean shot away and hit the side netting.
In the third and final minute of second half stoppage time, Craig Ross hit the ball low and hard over the top of the Notts County back line towards Alex Nicholls. The forward took a touch with his chest before firing past Collin and earning a much needed win for the Bees.
Attendance - 1752 (606 Notts County fans)
Barnet line-up: Ross, Brindley, Clough, Santos (Plavotic 83'), Watson, Weston, Akinde, Tutonda, Bover (Akinola 45'), Nicholls, Nicholson (Vilhete 82')
Unused: Legg, Coulthirst, J. Taylor, Sule.
Amber Big Draw - 05665