Luke Emery upset his former club as he fired the only goal of the game when Daventry Town beat Newport Pagnell Town 1-0 on Saturday.
The striker, who once called Willen Road his home, netted a penalty after just 10 minutes in a game which manager Darren Lynch said his team "did not turn up" to against the UCL Premier Division leaders, thus ending Town's four-match unbeaten run.
"I’m honest we never turned up," said Lynch. "As good as we’ve been over the last month or so we let ourselves down.
"Credit to them as they were first and second to everything all over the pitch and my disappointment was that we never gave a good account of ourselves and let all of our good work over our good period go without a fight.
"The game was decided with a penalty in the first 10 minutes and to be honest that was as good as the game got."
Town remain 10th in the table, and take on 11th place Leicester Nirvana on Tuesday night.