Relegation threatened Cambridge created eight excellent chances but still failed to beat local rivals Northampton at home for the first time in a league match since 1972.
They dominated the game, setting up chance after chance, but just as against Bristol in midweek lacked the luck and the judgement to get the point.
And it seemed almost inevitable as the game went into stoppage time that the curse of the Cobblers might strike again.
From their only corner of the second half Chris Willmott rammed a shot under the crossbar after goalkeeper Shaun Marshall could only palm away a Marc Richards header.
It should have been no more than a scrap of consolation for the out-played Northampton side, but it was just not Cambridge's day.
Striker Jermaine Easter, possibly playing his last match on loan from Hartlepool, could have had four goals alone.
He strayed offside before putting the ball in the net in the first minute, fired wide in the eighth, had a header pushed onto the post by goalkeeper Lee Harper in the 61st then blazed over the bar from only four yards in the 69th.
As well as the save from Easter, Harper did well to block an Adam Tann drive midway through the first half and on the one occasion when he was beaten by an Andy Duncan header in the 32nd minute, defender Paul Trollope cleared off the line.
Tom Youngs returning against his old team had Northampton's only other chance but was slow to shoot after breaking through in the fifth minute and had the ball taken off his toe by young defender Dan Gleeson.
Cambridge boss John Taylor tore into his team, commenting: "I am an angry man because despite having all of the game we threw it away again exactly as we did against Bristol.
"We've practised all week but we can't defend a corner to save our lives. We were unlucky not to score a goal or two but you just can't give things away at any stage of a match.
"It was a dreadful end for our supporters who stuck with us this week." Not surprisingly Cobblers boss Colin Calderwood said he was 'delighted' with the smash and grab three points.
He said: "We didn't play our best I accept that, but we were tougher than against Kidderminster in midweek, we hung in there against a good Cambridge team and we had the character to push up at the end and get the goal.
"This was a huge boost for our play-off hopes." Cambridge and Taylor look in big trouble now after three consecutive defeats in the space of eight days.