Chris Giles netted early in the second half to give the Reds their third victory on the trot.
The home side dominated the first half and almost took the lead after 12 minutes through Tony Scully.
The former Manchester City midfielder beat Gavin Heeroo for pace and chipped neatly over keeper Scott Howie, but covering defender Andy Duncan scrambled back to clear off the line.
Crawley went close again soon after when Omari Coleman had an angled shot parried wide by Howie after he was sent clear by Steve Burton.
Cambridge created just one clear chance in the opening 45 minutes when Jamie Guy headed wide unmarked on the half hour.
Crawley broke the deadlock on 55 minutes through a towering header by Giles. The defender rose above his marker at a Danny Brown corner and nodded a looping effort over the stranded keeper from the edge of the six-yard box.
The visitors played the last 22 minutes a man down after former Chelsea midfielder Rob Wolleaston was shown a second yellow card.
Scully squandered a golden opportunity to put the game beyond doubt on 72 minutes when he was sent free on goal by Burton. He tried to dribble round Howie instead of shooting and the keeper smothered bravely at his feet.
The home side dominated the first half and almost took the lead after 12 minutes through Tony Scully.
The former Manchester City midfielder beat Gavin Heeroo for pace and chipped neatly over keeper Scott Howie, but covering defender Andy Duncan scrambled back to clear off the line.
Crawley went close again soon after when Omari Coleman had an angled shot parried wide by Howie after he was sent clear by Steve Burton.
Cambridge created just one clear chance in the opening 45 minutes when Jamie Guy headed wide unmarked on the half hour.
Crawley broke the deadlock on 55 minutes through a towering header by Giles. The defender rose above his marker at a Danny Brown corner and nodded a looping effort over the stranded keeper from the edge of the six-yard box.
The visitors played the last 22 minutes a man down after former Chelsea midfielder Rob Wolleaston was shown a second yellow card.
Scully squandered a golden opportunity to put the game beyond doubt on 72 minutes when he was sent free on goal by Burton. He tried to dribble round Howie instead of shooting and the keeper smothered bravely at his feet.