Substitute Andy Robinson inspired the Swans to a crucial win which moved them back into the League Two automatic promotion places.
Robinson's second-half introduction proved the turning point
The midfielder opened the scoring on 66 minutes with a left-foot finish from the edge of the box before setting up top scorer Lee Trundle on 83 minutes.
Trundle put the result beyond doubt with his second five minutes later.
Bottom club Cambridge were woefully short of ideas in front of goal and are now nine points from safety.
Swansea: Gueret, Ricketts (Gurney 90), Austin, Monk, Iriekpen, O'Leary, Martinez, McLeod (Robinson 55), Britton, Trundle, Thorpe.
Subs Not Used: Bean, Connor, Forbes.
Goals: Robinson 66, Trundle 83, 88.
Cambridge Utd: Ruddy, Goodhind, Duncan, Tann, Newey, Somner, Nicholls, Toner (Latte-Yedo 80), Chillingworth (Turner 74), Roberts (Tudor 66), Bramble.
Subs Not Used: Blackburn, Quinton.
Ref: L Probert (Gloucestershire).