They caught Cambridge cold and took the lead with an angled strike from Jamie Cade after just three minutes. Crawley continued to look strong but were made to pay when slack marking allowed David Chick, back after two months out through injury and suspension, nodded home a left-wing cross by Ritchie Hanlon after 32 minutes.
Neil Jenkins hit the bar with a free-kick from the edge of the area as Crawley looked to regain their lead. But it was United who went in front in the 36th minute as Hanlon smashed home the ball into the bottom corner from 30 yards.
Cambridge's leading scorer Fola Onibuje missed with two headed chances either side of the half-time whistle, while Andy Duncan also had a header well saved by Crawley keeper Phil Smith.
The visitors piled on the pressure with Paul Armstrong shooting just wide and Jenkins firing well over fromr a free-kick around the hour mark.
And Crawley were virtually camped out in the Cambridge half in the last quarter of an hour.
Dave Woozley nodded inches over the bar, while Andy Lindegaard just failed by inches to get a touch on a dangerous low cross from Chris Giles.
Crawley could have had a penalty awarded against them in injury time when Woozley handled in the area, but the referee waved away Cambridge's appeal although there was not enough time for the visitors to get the equaliser their play deserved.
Neil Jenkins hit the bar with a free-kick from the edge of the area as Crawley looked to regain their lead. But it was United who went in front in the 36th minute as Hanlon smashed home the ball into the bottom corner from 30 yards.
Cambridge's leading scorer Fola Onibuje missed with two headed chances either side of the half-time whistle, while Andy Duncan also had a header well saved by Crawley keeper Phil Smith.
The visitors piled on the pressure with Paul Armstrong shooting just wide and Jenkins firing well over fromr a free-kick around the hour mark.
And Crawley were virtually camped out in the Cambridge half in the last quarter of an hour.
Dave Woozley nodded inches over the bar, while Andy Lindegaard just failed by inches to get a touch on a dangerous low cross from Chris Giles.
Crawley could have had a penalty awarded against them in injury time when Woozley handled in the area, but the referee waved away Cambridge's appeal although there was not enough time for the visitors to get the equaliser their play deserved.