The 1-0 defeat at the hands of Rotherham United hinged on a 65th minute incident which saw Cobblers man Craig Hinton sent off and home striker Adam Le Fondre convert the resulting penalty.
Although Ian Sampson's men, later reduced to 9 men, drop to 10th place in League Two, they remain just 2 points off the play-off places.
Reaction to follow on Cobblers Mad.