Barrow scored six minutes into added time to draw 1-1 and stop Cambridge moving top of Sky Bet League Two.
With added time up, defender Matt Platt headed firmly beyond Dimi Mitov to secure a point that the Bluebirds richly deserved.
David Dunn's side had bossed the first half and hit the woodwork twice, Harrison Biggins striking a freekick from almost 30 yards which beat Mitov but hit the post.
Three minutes before the break Josh Kay's shot from the left was almost diverted in for an own goal by Harry Darling, only for Mitov to turn the ball onto the underside of the crossbar.
Cambridge were gifted the lead 11 minutes into the second half when goalkeeper Joel Dixon, under pressure from Paul Mullin, passed the ball straight to Joe Ironside who fired into an empty net from the edge of the box.
Twenty minutes from the end Bradley Barry almost levelled things with a drive that Darling headed off the line with Mitov beaten, only for Platt to snatch a point at the death.