Conference Premier leaders Cambridge saw off Salisbury with a second-half double from substitute Kwesi Appiah.
The home side were stifled in midfield in the opening half and Brian Dutton almost headed Salisbury in front.
But the visitors failed to deal with a long ball soon after the interval and Appiah rolled the ball over the line.
The on-loan striker added his fifth in nine games since arriving from Crystal Palace by curling home from Arnold's pass in a slick counter-attack.
The victory extended Cambridge's unbeaten start to the season to 16 games, and maintained their six-point advantage at the top.
VIEW FROM THE DRESSING ROOM
Cambridge United manager Richard Money told BBC Radio Cambridgeshire:
"Because of where we are, people are going to come and try and test us in different ways. Are they going to come and sit and frustrate, or are they going to come and have a go? In fairness, they came and had a go.
"People know that most of the time we want to play 4-4-2 with a lot a movement, but sometimes you've got to change it.
"The first job for any coach or manager is to determine whether the opposition's shape is causing you a problem. In the first half, it was.
"We are juggling a bit at the moment, trying to get minutes in to people who are coming back."
Salisbury City manager Mikey Harris told BBC Wiltshire:
"Obviously I'm disappointed. In the first half we gave ourselves a platform to win the game. We knew the threat from them was going to be a ball flicked on, and we didn't deal with it.
"That was the turning point and again we switched off from our own set piece and they hit us on the counter attack.
"It wasn't to be today and we've only got ourselves to blame."
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