Robert Ogleby's late leveller rescued Wrexham a vital Blue Square Bet Premier point as their automatic promotion hopes were dealt a blow at Cambridge.
Tom Shaw's 20-yard strike had seemingly reignited Cambridge's play-off dreams when he shot low into the corner of Wrexham keeper Joslain Mayebi's net.
Mayebi made stunning saves from Harry Fell's header and Michael Gash's strike as Cambridge looked to be in control.
But Wrexham equalised when Ogleby fired home from close range.
The Wales Under-21 striker pounced on Mark Creighton's knockdown in the fourth minute of added time to fire past Danny Naisbitt for his first Wrexham goal since joining in January.
Substitute Ogleby's effort was Wrexham's only real goal chance as top-of-the-table to extend their lead to eight points although second-placed Wrexham do have a game in hand.
Wrexham manager Andy Morrell said: "We didn't really deserve to win the game today.
"That late goal might be important but we needed to win and it took the goal to spark us into life and we had two minutes of testing them out and that is not good enough in a 90 minute game."