Ben Thatcher and Steve McManaman made surprise appearances for the Blues and confirmed their return to fitness by coming through unscathed.
Christian Negouai opened the scoring after 11 minutes from a Willo Flood corner, before missing a host of chances, although he netted a second with 20 minutes remaining when put through by Stephen Ireland.
Bradley Wright-Phillips was denied by keeper Ben Smith in the second half but scored City's second with his 17th goal of the season after latching onto Thatcher's long ball.
Young substitute Ishmael Miller hit two more in the last five minutes to boost City's goal difference. First he converted a penalty after being brought down by the keeper, and he held off a defender to score the other following Flood's through ball.
City remain 3 points behind United at the table and, despite this scoreline, still have a much superior goal record than the Blues.
City: Weaver, Warrender, Thatcher, J D’Laryea, Richards, Sommeil, Croft (Ireland 62), Flood, Negouai (Miller 78), B Wright-Phillips (Bermingham 76), McManaman. Subs: Schmeichel (GK), Collins.
Newcastle: Smith, Gate, Cave, Farman, Huntington, Edgar, Brittain, Finnigan, Walton, A O’Brien, Terrell. Subs: Baxter, Carroll, Cavener.
Attendance: 545.