Darlington manager David Hodgson was fuming as his team slipped into the relegation zone with their worst performance since he returned to the club five weeks ago.
The defeat was narrow, being decided by a dubious penalty, which gave Cambridge their first home win since the opening day of the season.
But the performance of his side enraged Hodgson.
He said: "I want answers from the players. Even though we beat York 3-0 last week they dominated us for 25 minutes. On Saturday Cambridge dominated the opening 45.
"We cannot allow that to happen, and the players must look at themselves and ask themselves why Cambridge were first to every loose ball.
"The midfield concerned me most. We didn't click at all."
Cambridge led courtesy of a Luke Guttridge penalty in first-half injury time after Craig James was adjudged to have pushed player-manager John Taylor as a cross appeared to be heading harmlessly over.
"The goal is irrelevant," said Hodgson. "You get decisions like that. Rather than ask the referee why he gave it, I'd rather get an answer from the players as to why they allowed Cambridge to get the ball from one end of the field to the other without us getting a challenge in.
"There were only four or five players to emerge with any credit and there is some serious hard work to do on the training ground this week."
Keeper Michael Price escapes criticism, as do central defenders Craig Liddle, Joey Hutchinson and star man Matt Clarke.
New striker Lee Matthews in his first game did what could be expected.
But every other player was short of his best, and in a battle against relegation, there is no scope to carry anybody.
Neil Wainwright missed an injury-time chance to equalise when he delayed his shot when through on goal, adding to the gloom.
And the club's financial position gives Hodgson little scope for change.