There was little invention or inspiration displayed by either side for most of the match which was mainly notable for referee Russell Fletcher's eight yellow cards and one red.
It was never, however, a kind of battle the bookings suggested as the game drifted along with very little goal mouth action.
Gravesend grabbed the lead from just about their only first half attack thanks to the expertise of Jimmy Jackson at set pieces. After team-mate Bobby Bowry had been booked for taking the kick too soon Jackson stepped up to hammer a 30-yarder through the disorganised defence and low inside the left-hand post.
Cambridge went close to levelling in the 38th minute when Dan Gleeson's shot rebounded off the post. That piece of action followed a frantic five minutes in which referee Fletcher for some reason made four bookings.
Gravesend might have wrapped things up early in the second half, but Jackson had a couple of free-kicks well saved this time by keeper Scott Howie.
When Cambridge looked as though they might breakthrough, Fola Onibuje was brought down in the 67th minute by Paul McCarthy who got his marching orders for the foul.
Ten minutes later though Onibuje headed down a Jon Brady cross, Craig Holloway palmed the ball out and Courtney Pitt rifled an equaliser into the roof of the net.
In stoppage time Cambridge's Mbiyeye Medine headed wide from close range before Craig Westcarr blazed over.