Plucky Cambridge clung on for a point against all the odds after Hull's Jamie Forrester had equalised Tom Youngs’ opener.
Hull opened the brighter and John Anderson's flick on fell for Forrester only for keeper Shaun Marshall to block superbly.
At the other end a low drive from Daniel Chillingworth was well held by Alan Fettis, but it was the home side who were forcing all the pressure.
Stuart Elliott just failed to connect properly from close range allowing Marshall to smother the ball, and then Lawrie Dudfield, fired a shot across the face of goal when put clean through by Anderson's long ball.
Cambridge - who went into the game without top scorer Dave Kitson, and who started with a reshuffled back four - were then dealt a blow when Chillingworth hobbled off after just 18 minutes to be replaced by Francesco Nacca.
Almost immediately Nacca's low shot was saved by Fettis and then the dangerous Omer Riza provided further respite for the visitors by belting a right foot shot over the crossbar.
Hull's Elliott was tormenting the United defence, and twice superb work down the left carved out opening for Dudfield, who could not take full advantage.
To sum up the home side's misfortune Dean Keates clipped the inside of the post with a low left-foot shot in the dying seconds of the first half.
The match burst into life in the opening minutes of the second half and Adam Tann was ordered off for elbowing Elliott on 48 minutes.
Just two minutes later Hull took advantage when Tom Newey clattered into Richard Appleby, and Forrester converted the resultant penalty by sending the keeper the wrong way.
Hull substitute Ryan Williams and Anderson both came close for the home side, but Youngs could have nicked it for the visitors, but his powerful long-range effort was well saved by Fettis.