A first-half goal from Dave Bridges earned Cambridge their first away win of the season.
Bridges struck after just 16 minutes of a tough game to shock a home side who had yet to lose on their home patch this campaign.
Both teams started well with Cambridge defender Andy Duncan making a vital intervention to deny Michael Twiss a free run on goa,l and Garry Thompson's dangerous low cross well cut out by Scott Howie in the first five minutes.
At the other end Stephen Smith's long throws were causing the Morecambe defence a number of problems, and on-loan left-back Danny Bunce curled a free kick over before the vital goal.
Bridge found himself in space on the right-hand side of the Morecambe box and he let fly with a superb, low, shot that gave Ryan Robinson no chance as it sneaked just inside the right-hand post.
The game became something of a midfield war with some tough tackles from both sides leading to a string of bookings before Morecambe, unbeaten in seven league games at Christie Park before the game, threatened again.
Howie came to the U's rescue on 35 minutes with a stunning save to deny Ged Brannan a debut goal as he worked wonders to block a close range header from the midfielder.
The second half began with Cambridge on the attack again as Mark Peters' clever overhead kick fell just wide of the left-hand post wit Robinson beaten.
But then Morecambe hit back again as Thompson, the Shrimps' biggest threat, rose well to meet a left wing Howard cross but saw his looping header hit the crossbar with Howie beaten.
As the Shrimps pushed forward Cambridge thought they had made it 2-0 when Paul Atkins ran on to a through ball and lobbed Robinso,n but the play was brought back for an offside, much to the disgust of the U's boss.
It was a decision that could have proved to be vitally important as Morecambe wasted two glorious opportunities to level in the dying stages.
With 10 minutes to go David Perkins was all alone six yards out but he skewed his shot horribly wide before Wayne Curtis was presented with a golden opening by Michael Twiss's flick, but he also made a hash of his effort and missed the target completely.
There was still time for more drama in injury time as on-loan West Ham defender Bunce was sent off for a second yellow card after blocking Thompson crudely, but the visitors held on to record an important win.