Defeat in Suffolk
Town fell to their first defeat at home since November as Cambridge claimed the three points at Portman Road.
The deciding moment, which went down as a Dom Thompson own goal, came early in the second half as the Blues' play-off hopes were dealt a blow.
Kieran McKenna made two changes from the previous weekend’s victory over Plymouth as Tom Carroll and Conor Chaplin returned to the starting XI.
The duo they replaced, Tyreeq Bakinson and Sone Aluko, were both on the bench whilst Idris El Mizouni was also named amongst the substitutes.
Town had the first effort on goal within two minutes at Portman Road, Dimitar Mitov comfortably collecting Bersant Celina's low shot.
Cambridge had the ball in the back of the net with just under quarter of an hour played, but the linesman’s flag was up before Joe Ironside fired a flicked-on cross into the roof of the net from close range.
Christian Walton had to be alert a few minutes later as the U’s went close again, Town's 'keeper tipping George Williams' header over the top of the bar following Adam May's corner.
A well-worked move created the next chance for the Blues, but Sam Morsy’s prodded effort following a pinpoint low cross from Thompson did not have enough on it to beat Mitov.
Cambridge had the first chance of the second period, Walton getting down well to his right to push away Lloyd Jones' goalbound header.
Town responded well and, a minute later, created a great opening of their own but Chaplin's fizzed effort across the face of the goal was out of the reach of the sliding James Norwood.
The visitors took the lead on 56 minutes. A free-kick from the corner of the box found its way to the back post, where the ball came off a combination of Ironside and Thompson and ended up in the back of the net, with the Blues’ defender appearing to have the final touch.
A good reaction stop from Mitov prevented an equaliser shortly afterwards, the U’s number one blocking Norwood’s half-volley from a narrow angle with his legs after the Town forward had been found with a lofted pass from deep.
Macauley Bonne, introduced alongside Aluko midway through the half, headed onto the roof of the net as Town continued to pursue the leveller, with Ironside blasting wide from just inside the box at the other end a few moments later.
The Blues looked to have grabbed a stoppage-time equaliser when the ball was forced home following a goalmouth scramble but the linesman's flag was up and Cambridge saw out the closing moments to claim the spoils.
Town: Walton, Donacien, Woolfenden, Burgess, Burns, Carroll (Aluko 64’), Morsy (C), Thompson (Penney 73’), Chaplin (Bonne 64’), Celina, Norwood.
Subs: Hladky, Bakinson, El Mizouni, Pigott.
Booked: Norwood, Donacien, Woolfenden, Bonne.
Cambridge: Mitov, Williams, Digby (C), Jones, Brophy (Sherring 90'), Ironside, Smith, Dunk, Okedina, May, Knibbs.
Subs: Mannion, Iredale, Hoolahan, Tolaj, Lankester, Worman.
Booked: Smith, Dunk, May.
Attendance: 26,515 (2009 Cambridge fans).