Vincent Kompany's thumping first half header has sent Manchester City top of the Premier League at the expense of bitter rivals Manchester United at the Etihad Stadium.
The Belgian skipper evaded the attention of Chris Smalling to nod City into a lead in stoppage time in the opening 45 minutes.
United pressed for an equaliser in the second period, but the forlorn figure of Wayne Rooney, who rarely threatened, was indicative of a miserable evening for the 12-time champions, who have surrendered a eight-point lead at the top in less than three-weeks, as City go top on goal difference with two games remaining.
Build as the biggest Premier League fixture in the division's 20-year history and the most talked about Manchester derby in modern era the league's pacesetters collided in a game which would have significant implications on the destination of the title.
While City were unchanged from their win over Wolverhampton Wanderers, United adopted a European-style formation, with Ji-Sung Park starting his first league game for three months, as Antonio Valencia, Ashley Young and Danny Welbeck were left out from the start.
The reigning champions began the side the better, with Michael Carrick's goal-bound shot being blocked by Kompany and Nani blazing over when well placed.
Intent on allowing the hosts no time in possession, United's midfield trio of Paul Scholes, Park and Michael Carrick dictated the middle of the park in the early stages.
It wasn't until Samir Nasri committed United defenders that City had some joy in the final third, with Carlos Tevez's driven cross being turned away by Phil Jones.
With a three-point deficit to make up before the start of play, City had to continue to commit bodies and the first glimmer in front of goal saw Aguero smash a volley over David de Gea's goal.
The Argentine international almost finished off another sweeping City move, as Roberto Mancini's side began to dominate, as his skrewd effort came after Nasri found space on the right.
As dangerous as they were playing in front of United, the home side looked a threat in the break also, but Aguero's shot from a tight angle was all they could muster following Tevez's marauding run.
And in the dying embers of the first half City grabbed a deserved lead through Kompany's head from David Silva's corner.
United came out of the traps in the second half, bringing Danny Welbeck on to replace Park, handing Sir Alex Ferguson's side the impetus but the England international couldn't meet Rooney's cross before Jones' centre evaded everyone attacking in red.
The tension on the pitch threatened to spill over on the touchline, as Ferguson made his feelings felt to opposite number Mancini after substitute Nigel de Jong's foul on Welbeck.
Toure, Nasri and Gael Clichy could have settled the contest for City, but were denied, as at the other end United toiled against the home side's dogged back-four, and even with five minutes added on time, couldn't grab a crucial leveller to sen the initiative in the title race swung the way of the blue half of Manchester.