Poor defending cost Lincoln City the chance to secure a third consecutive win.
The Red Imps should have notched up a comfortable victory but conceded two sloppy goals and finished up hanging on for a point.
But the result delighted Cambridge whose manager John Taylor said: "We know when we play Lincoln we are not going to get many chances but we created quite a few.
"We played well in patches and it was a good afternoon's work. Although we're pleased with an away point we're disappointed because we dominated the second half and should have won the game." Lincoln got off to a great start when striker Gary Fletcher made the most of an error by Cambridge skipper Andrew Duncan to flick home a shot off the underside of the bar in the eighth minute.
Four minutes later City went close again when Peter Gain put Mark Bailey in the clear but the defender sent his shot straight at Cambridge keeper Shaun Marshall.
Cambridge were level in the 14th minute when Luke Guttridge caught out the Imps defence with a quickly taken free kick and his low shot was pushed into the net by the despairing dive of Lincoln keeper Alan Marriott.
Cambridge player-manager John Taylor then hit the post from the narrowest of angles after some excellent work by teenage striker John Turner.
Turner was involved again on the half-hour when he set up on-loan midfielder Neil McCafferty but the United man's shot was kept out by Marriott.
Lincoln were back in front four minutes before the break thanks to the persistence of Fletcher. His first shot was pushed out by Marshall but the striker reacted quickly to slot home the rebound for his tenth goal of the season.
Lincoln substitute Simon Yeo smashed a 70th minute shot against the bar when it looked easier to score and then wasted another late chance when he was put clean through but saw his shot saved by Marshall.
Cambridge scored the goal of the game in the 88th minute to level things up. Turner, who gave an impressive performance for a 17-year-old, sent over a perfect cross which was converted from close range by Daniel Webb.
Then in stoppage time Cambridge swept through again. Substitute David Bridges put the ball into the six-yard box but Paul Morgan hacked the ball away as Webb lined himself up for the winner.