The game was billed as a huge clash in the League One relegation battle with two of the bottom-three sides going up against each other.
Shayne Lavery's first-half double was added to after the break by Dan Nlundulu and Elias Kachunga, with John Marquis' penalty proving scant consolation.
The victory lifts the U's to three points from safety, while Ainsworth's Shrews sit bottom and eight points adrift of the dotted line.
Ainsworth said: "Defensively, I can see now why the team is really struggling.
"We were very poor defensively today. Cambridge haven't ripped us apart with football, it's been basic stuff.
"Two throw-ins they've got in on, which is criminal. A free-kick, we're just not alive.
Denne historien er fra December 08, 2024-utgaven av The Football League Paper.
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Denne historien er fra December 08, 2024-utgaven av The Football League Paper.
Start din 7-dagers gratis prøveperiode på Magzter GOLD for å få tilgang til tusenvis av utvalgte premiumhistorier og 9000+ magasiner og aviser.
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RAVENS FLY TO STORMY SUCCESS
ANDY Woodman admitted Bromley's win over Accrington is a game his victorious side 'will never watch back again'.
U'S TAME THE A FAST START
GARETH Ainsworth was dismayed with Shrewsbury's defending as his side were beaten by a rampant Cambridge, in a game which included a goal in the first minute of both halves.
SUPER BLUES' JAY AT DOUBLE
JAY STANSFIELD bagged the plaudits for Birmingham with a brace as they hit back to beat ten-man Barnsley in front of 5,000 travelling fans at Oakwell.
MATT'S ODE TO JOY FOR DETERMINED CHAIRBOYS
Royals in recovery with boss departed
IT JUST EXPLODED OUT OF NOWHERE - IT WAS WILD!
SHEFFIELD United v West Brom? For fans of a certain vintage, it's a fixture that can only conjure one memory.
ROHL RAGES WITH HIS SLOPPY OWLS
DANNY Rohl ripped into his Sheffield Wednesday side after they were held at home by Preston.
ACE KEEPER KAMINSKI IS THE BIG DIFFERENCE
LUKE Williams insisted that his Swansea City side could well have left with all three points after being denied victory by home keeper Thomas Kaminski.
Kolli is Marti's new Ray of sunshine
PROUD QPR boss Marti Cifuentes is hoping Rayan Kolli's maiden senior goals prove to be \"the first of many\" after the youngster played a starring role in the victory over Norwich.
FIRST WIN FOR FRANK AS LIONS ARE TAMED
COVENTRY head coach Frank Lampard felt his players took the game by the scruff of the neck after half-time the Sky Blues.
EUSTACE SALUTES BATTLING ROVERS
But a lot to ponder for Selles