Chesterfield goalkeeper Aaron Ramsdale gifted Stevenage a goal after a poor clearance rebounded off Ben Kennedy to bobble over the line.
As the Stevenage backline lumped the ball upfield following a Spireites attack, Ramsdale rushed from his 18-yard box in an attempt to clear the potential danger the loose ball threatened.
However, the clean connection on the ball that the 'keeper had anticipated never materialised and when the weak clearance hit the chasing Ben Kennedy, there was only going to be one outcome.
Kennedy sprinted to the line to ensure the ball crossed and despite Ramsdale's last-gasp slide tackle, it wasn't enough to stop the forward netting the winner three minutes into the second half.
Click on the video above to see how Ramsdale's mistake gave Stevenage victory at the Proact Stadium.