Michael Woods scored his first goal since the second Saturday of the season to end Hartlepool United's wait for an away win.
The midfielder slotted his shot past Will Norris in the 63rd minute to sink Cambridge, a result which lifted Pools two places and nine points above the relegation zone.
Pools went into the trip to play-off outsiders Cambridge having taken two points from a possible 36 on the road since winning 3-0 at Grimsby on the opening day of October.
But Dave Jones, who has overseen five defeats in a row since replacing Craig Hignett at the Northern Gas & Power Stadium, will have been thrilled by his side's display at the Abbey Stadium
Pools had a pre-match boost when Walker passed a fitness test on an ankle injury.
Walker, outstanding since his conversion from midfield into defence, missed Saturday's defeat at Notts County, but returned to partner Scott Harrison, with Lewis Hawkins dropping down to the bench.
And the 20-year-old enjoyed a first-half stroll as Pools dealt with a Cambridge side brimming with confidence after a 3-0 victory at promotion hopefuls Carlisle on Saturday.
Cambridge included former Pools left-back, Jake Carroll, and the Irishman seemed to forget he had swapped clubs in the transfer window when he played what appeared a backpass to Joe Fryer.
The U's offered little threat and the only effort on goal in the lifeless early exchanges came from Nathan Thomas whose 30-yard free-kick landed on the top of Will Norris's net.
Rhys Oates, Pools man of the match in the last two games, threatened when he made good ground down the left but his cross was massively over-hit.
It was to be his final contribution before limping of in the 33rd minute, Nicky Deverdics replacing him.
The U's did pick up their game as the half wore on, Leon Legge's towering header from Carroll's deep free-kick flashing just wide of Fryer's right stick.
And Luke Berry was the next to have a go at the away goal when he headed wide after good work down the right by former Pools loanee Brad Halliday.
Pools made a sharp start to the second period when Richardson played in a great ball from the right following an excellent attaclking move, but Cambridge managed to scramble it away.
The away side went close to a goal, courtesy of the hosts, when Legge almost headed past his own keeper but Norris produced a spectacular saves diving to his left
But Pools did not have long to wait to score and it was a beautifully-crafted goal.
Lewis Alessandra found Padraig Amond who looked suspiciously offside. But the pair combined nicely to find the on-rushing WOODS who finished with aplomb from nine yards.
There were ironic cheers from the home fans in the 67th minute when the U's had a shot on target, Clark's grasscutter easily collected by Fryer.
Cambridge went closer soon after when Piero Mingoia's cross was met by sub Paul Lewis but his header was cleared off the line by Harrison.
But it got better for Pools when the home side were reduced to 10 men, when Clark's late and poor tackle on Deverdics earned a straight red card by Mr Whitestone.
Pools had appeals for a penalty rejected in the 73rd minute when Scott Wharton seemed to handle from Deverdics who then put a free-kick over the bar.
And Pools went close 10 minutes from time when Thomas flashed a shot wide.
Cambridge had appeals for an injury-time penalty waved away when Lewis went down from Walker's cxhallenge.
CAMBRIDGE UNITED 0
HARTLEPOOL UNITED 1
Cambridge: Norris, Wharton, Halliday, Legge, Dunk (Maris 59), Mingoia, Dunne (Lewis 60), Clark, Berry, Carroll, McDonagh (Elito 46).
Subs not used: Roberts, Williamson, Taylor, Gregory
Sent-off: Clark 71
Pools: Fryer, Richardson, Walker, Harrison, Donnelly, Featherstone, Woods, Alessandra, Thomas, Oates (Deverdics 33), Amond.
Subs not used: Bartlett, Martin, Hawkes, Hawkins, Orrell, Rooney.
Goal: Woods 63
Booked: Richardson 31, Woods 61, Alessandra 84, Thomas 86
Referee: Dean Whitestone