Cambridge inflicted a third home defeat of the season on Newport with a 1-0 win at Rodney Parade.
The hosts dominated territory and possession, but Liam O’Neil struck in the second half to put a dent in Newport’s play-off bid.
Newport were in control for the majority of the first half and came close on two occasions, with Jamille Matt forcing a save from Callum Burton and Ryan Inniss heading just wide after being found unmarked.
The home side started the second half strongly, with Joss Labadie wasting a golden opportunity as he shot over the bar with the goal at his mercy.
Despite Newport’s territorial dominance, O’Neil nudged Cambridge ahead in the 68th minute as he rolled the ball into the back of the net after an initial shot by Paul Mullin deflected off goalkeeper Tom King into his path.
County threw everything at their visitors, but substitute Tristan Abrahams hooked his shot just wide from a good position as their push for an equaliser fell short.