A first-half goal from David Bridges was enough to hand Cambridge maximum points against 10-man Stevenage.
Both sides had chances in the early stages but after 20 minutes Craig Westcarr's cross found Bridges, who headed his sixth goal of the campaign.
After the break the home side were indebted to keeper Scott Howie, who denied George Boyd and Darryn Stamp.
Robert Quinn rattled the bar from close range before Ollie Berquez saw red late on for a second bookable offence.
Cambridge Utd: Howie, Duncan, Peters, Morrison, Heeroo, Bridges, Smith, Hanlon (Porter 78), Chick, Onibuje, Westcarr (Pitt 90).
Subs Not Used: Atkins, Bunce, Davies.
Booked: Onibuje, Smith, Duncan.
Goals: Bridges 19.
Stevenage: Julian, Warner, Quinn, Laker (Gregory 85), Perpetuini (Williams 76), Berquez, Brough (Lewis 66), Henry, Boyd, Nurse, Stamp.
Subs Not Used: Gore, Hocking.
Sent Off: Berquez (90).
Booked: Berquez, Laker, Warner.
Ref: R Lee (Brentwood).