Cambridge United reverted to type after Saturday's victory over Bristol Rovers, slumping, or rather slithering to a lame defeat in torrential rain.
They fell behind four minutes before the break and never looked like scoring before or after Eric Sabin's goal for Northampton Town.
The U's only managed a couple of shots on target as their dreadful record stretched to 13 league games and only nine goals.
At least the winner was a quality product, Sabin getting first to a left-wing cross to send a glancing header from the edge of the box flying high inside the far post.
The Cobblers were in control for virtually all of the second half as they gained in confidence after their recent shaky run.
They could have had more goals with a little bit more luck and judgment, David Rowson blazing over when well placed in the 62nd minute.
In the last five minutes ex-Cambridge striker Scott McGleish somehow headed wide from a couple of yards out then blazed over the crossbar from near the penalty spot.
The Cambridge fans, who booed their side from the pitch, could hardly remember their side's best effort, a shot from Dan Chillingworth in the third minute which the visitors' keeper, Paul Rachubka, did well to deflect for a corner.