The scoreline did not begin to tell the tale of a match in which United were overpowered, outplayed and outgunned in front of easily their biggest home attendance of the season.
Manager Quinn must have thought he had at least instilled some steel into the side during his month in charge after seeing United drive out a victory in midweek.
But that kind of doggedness was nowhere to be seen as Cambridge sleepwalked through a scrappy first half and then virtually surrendered as Crawley took complete control after the break.
Their attacking play was streets ahead of the hapless home team and they had the man to finish their good work in ruthless Scott Rendell, who took his tally to five goals in two consecutive Saturdays.
Crawley had hit the woodwork twice and gone close to scoring on two or three other occasions before Rendell struck to wrap things up in the 68th and 77th minutes.
Each time he was ably assisted by striker Jake Edwards who tirelessly and unselfishly did the hard work.
In the build up to the first goal, he held off a challenge from two defenders as he worked his way along the byline before cutting the ball back to Lee Blackburn who helped it on to Rendell who hooked it high into the net from seven yards.
Nine minutes later he was virtually unopposed as he broke away down the left, but seeing that Rendell was better placed in the centre, stroked a pass to him for his team-mate to lash the ball past the helpless keeper.
The two-goal margin was well deserved by the visitors who could have been out of sight by that stage.
Rendell slipped when going for goal in the 11th minute, Edwards had a shot blocked on the line in the 13th, Ben Strevens hit the crossbar in the 47th and Edwards had a shot pushed on to the post by the keeper in the 75th.
Unfortunately for Cambridge it was an afternoon in which they had given away more than a 1,000 tickets to residents and workers in the vicinity of the stadium in a bid to promote the club.
But the additional supporters had to wait until the last 12 minutes for anything to cheer and then it was only near misses and wasted opportunities.
Cambridge should have got the goal which would have made it a thrilling finish when Danny Carey-Bertram found himself clear in front of goal only to blaze over the crossbar with goalkeeper Ben Hamer at his mercy.
A couple of minutes later Carey-Bertram again managed to burst through what looked like a tiring defence only to see his 20 yarder slam against the right-hand post.
With Crawley beginning to panic a little, Cambridge threw everyone forward but could not get the breakthrough until it was much too late.
Winger Jon Brady, who Crawley had set out to nullify because of the danger of his pin-point crosses, at last managed to find some space and when he did he hit a 25 yarder which whistled past the keeper into the roof of the net.
But that was in stoppage time with less than a minute remaining and it was too little too late.