United ended a run of four successive derby defeats and addressed the recent imbalance between the sides with a dominant 4-2 victory over our neighbours.
The win moved the Reds back to within a point of second placed Arsenal and stretched our advantage to four points over City after weathering an early storm from the fading Premier League champions.
City, who had lost their last two away games at Liverpool and Crystal Palace, made a blistering start and took an early eighth minute lead.
David de Gea had saved well from Jesus Navas, but the Spanish stopper was powerless to prevent Sergio Aguero scoring from close range.
The Argentine, so often a scourge of United, converted David Silva's cutback after superb build-up from James Milner.
The Reds were on the ropes against the visitors fast start but responded quickly and drew level just six minutes later.
De Gea's long clearance picked out Ander Herrera who in turn picked out Ashley Young who reacted first to stab in the rebound after Gael Clichy blocked his initial effort to send OT into ecstasy.
The in-form winger then turned provider as United turned the game on its head just before the half-hour mark when Young's cross was met by Marouane Fellaini, who steered home his header past Joe Hart, who should really have done better.
The tide continued to flow United's way and Hart made amends shortly after the re-start when he kept City in the game with a fantastic double save to keep out first Wayne Rooney and then Michael Carrick when both had looked certain to extend United's lead.
The reprieve was only temporary though, as we deservedly moved 3-1 ahead on 67 minutes when Rooney's wonderful reverse pass released Mata, possibly marginally offside, and he lashed in from a narrow angle.
Things got even better for United seven minutes later when Smalling emerged unmarked to glance home his header from Young's free-kick and send the Reds into dreamland.
Aguero scored in the closing moments to add a touch of respectability for City but this did nothing to sour a magnificent derby day for United, our sixth successive win.
Manchester is Red!
United Faithful Man of the Match: Everyone was again outstanding but Ashley Young gets MOM this week as he scored one, set up two and was a constant menace to the City defence.
Overall team performance: 8.5/10