For an hour it looked as though the visitors would have little trouble defending their impressive record of losing only four times on their travels this season, even if they lacked the fire power to get the win.
But in the 61st minute veteran forward Martin Carruthers broke away down the left and sent in an awkward cross which goalkeeper Shane Higgs could only palm into the path of Shane Tudor who rammed the ball back past him from five yards.
It was only Cambridge's second real threat after the 60th minute free-kick which produced a header from Danny Webb which skimmed the crossbar.
Cheltenham dominated possession almost carving out as many shooting opportunities as they had against Oxford at the weekend when they totaled 23, but the cutting edge just was not there.
Even when they hit the target they found teenage goalkeeper John Ruddy at his best.
Cheltenham's Damian Spencer broke through in the 15th minute only to slam a shot straight at Ruddy, and when he looked certain to score a minute into the second half after running onto a Brian Wilson cross, Ruddy produced a brilliant point-blank block.
Too often Spencer and his fellow strikers Steve Guinan and Martin Devaney failed to hit the target as good approach work was squandered.
Cambridge never looked like adding to the goal which ended their three-month and 15 match wait for victory, but the confidence of being ahead was obvious in its effect as they matched the promotion challengers for the remainder of the game.
Just before he was substituted Spencer had one last chance to snatch an equaliser for the Robins but he was stopped by a determined challenge from centre-back Andy Duncan as Cambridge held on to a vital victory.