Angry Shrewsbury boss Kevin Ratcliffe called on his shambles of a side to "shape up quickly if we are not going to go out of the League".
The former Everton defender was appalled by the sloppy display which allowed a Cambridge side, on a run of six games without a victory, to stroll to their biggest win of the season.
From the time Dave Kitson headed Cambridge in front in only the fourth minute the East Anglians dominated completely, virtually wrapping it up with goals either side of half time and playing keep ball for much of the second half.
Omer Riza made it 2-0 when he sliced through the middle of the worst defences in the division, taking their goals against tally at that stage to 52.
Riza was the provider two minutes after the break enabling Tom Youngs to head in from point-blank range.
Kitson was the same distance out when he stabbed the ball in on the hour from another Riza cross and the rout was completed nine minutes from time when Youngs was unmarked at the far post when the corner came over from Tony Scully.
Nothing was seen of the 28-goal Shrewsbury strikeforce of Luke Rodgers and Nigel Jemson, apart from a couple of runs in each half easily stopped by what was a makeshift injury-hit Cambridge defence.
Said a delighted Cambridge boss John Taylor: "That's re-launched our promotion bid. We haven't been playing that badly despite the result but we needed this kind of display for our confidence.
"We were on top right from the start and it was the quality of the football which most pleased me." Said Ratcliffe: "That was our worst performance of the season, we just can't defend.
"We have to start communicating more, cut out the niggling and play with a bit more discipline. We had seven players booked and although some were a bit harsh, you have to realise how a referee is going about his game.
"Just as disappointing was the fact that our attack was not on-song at all when a goal before their second in the first half could have changed the game."