Two goals in nine minutes late in the game ended Grimsby Town's ten-month wait for an away win.
After a dreary stalemate during the first half it was Grimsby who made the breakthrough, out-gunning a toothless Cambridge team who were booed from the pitch by the home fans.
Neither side forced a saved from the keeper during the first half, each squandering their only chance in the early stages.
Adam Tann scooped a shot over the bar from close range in the third minute and Grimsby's Andy Parkinson fired straight at a defender eight minutes later.
It wasn't until the 63rd minute that Cambridge managed their first shot on target.
That John Turner effort had no venom, unlike the shot from Parkinson two minutes later that flew past the keeper and into the roof of the net.
Grimsby took over completely after the goal, carving out an easy second in the 74th minute.
Cambridge keeper James Jowsey, making his league debut, was let down by his defence who allowed Michael Reddy to run unchallenged through the middle before setting up John McDermott for his first goal in eight years.
The U's looked as though they could play that long without scoring, Turner raising the only hope amongst the home fans when he broke through seven minutes from time only to have his shot plucked out of the air by the under-worked Tony Williams.