Michael Gash scored for the fourth successive game as Cambridge extended their unbeaten run to eight games with victory over Braintree.
The U's began the stronger, with Kevin Roberts and Harrison Dunk both firing early efforts off target.
The visitors almost took advantage when Dan Holman's effort squeezed just over the bar.
But Gash scored the decisive goal when he turned in Rossi Jarvis's cross to finish a flowing move from the hosts.
VIEWS FROM THE DRESSING ROOM
Cambridge United head coach Richard Money told BBC Radio Cambridgeshire:
"That is the biggest and best win since I have been here.
"The pitch was soft and drying and there was no pace in the pitch, so it was difficult to move the ball quick enough, and for 20 minutes we were outstanding.
"The most important thing today was the result and we said at half-time let's make sure one is enough to win it, because it looked like that type of day and we showed great resilience."