Manchester City won a chaotic derby at Etihad Stadium as Sergio Aguero's second-half strike gave the Premier League champions victory over Manchester United.
Aguero's 10th Premier League goal of the season finally breached a depleted United defence after Chris Smalling had been sent off in the first half and Marcos Rojo taken off on a stretcher after the break with shoulder damage.
It also brought a shaft of light to a disappointing week that had seen manager Manuel Pellegrini's side lose at West Ham in the league then see their Capital One Cup defence ended at home by Newcastle.
In a game that was played on the edge of ill-discipline and often strayed into it, Aguero's goal will also have come as a relief to City and their fans who were infuriated at seeing a succession of presentable penalty appeals rejected by referee Michael Oliver.
Most significantly, it kept leaders Chelsea in the champions' sights, albeit with a six-point advantage and four ahead of second-placed Southampton.
This was a compelling derby, the first for new United manager Louis van Gaal, who saw his defence stripped bare and the attacking riches of Angel Di Maria, Robin van Persie and Wayne Rooney - returning from suspension - fail to fire.
The Dutchman will be furious at the unnecessary way in which Smalling was dismissed, while the hosts will be happy their mini-slump was ended by a sixth win in the last seven Manchester derbies in the Premier League.
Nerves and tempers were frayed towards the end as United mounted a recovery of sorts and while this was not the sort of display to have Jose Mourinho and Chelsea looking anxiously over their shoulders, victory was all that mattered to City after recent mishaps.
Such was the combustible nature of the first half, with quality at a premium, that it was inevitable players from both sides would be running the risk of a red card.
Rooney harangued referee Oliver to demand a booking for Pablo Zabaleta while England keeper Joe Hart was right in the official's face when Daley Blind kicked the ball away having already been booked.
Amid the mayhem, United keeper David de Gea demonstrated his growing stature with a superb reflex save from Jesus Navas before diving bravely at the feet of Aguero, both players collecting an injury in the process.
When the red card came, it was in the most irresponsible manner imaginable. Smalling had been needlessly booked for charging down Hart's clearance then launched himself at James Milner in a manner that was only going to end one way.
The centre-half was studiously ignored by United's management team as he made his way off, Michael Carrick replacing Adnan Januzaj as Van Gaal was forced into a defensive redesign.
Temperatures were rising on and off the pitch as referee Oliver refused to answer several home demands for penalties, particularly when Fellaini clashed with Aguero before half-time and again after the interval when he attempted to dart between the Belgian and Carrick in the area.
United's defensive resources were further reduced when Rojo was taken off on a stretcher after damaging his shoulder diving into a challenge on Martin Demichelis. Teenager Paddy McNair came into a makeshift rearguard.
It was impossible to see the visitors keeping City out - and they did not. The breakthrough came after 62 minutes when Yaya Toure's pass cleared space on the left flank for Gael Clichy, whose cross was met expertly by Aguero, pulling away from defenders to flash a powerful finish high past De Gea.
Navas struck a post as City tried to confirm their advantage but suddenly, against all odds, United became a threat as Hart saved from Van Persie and Di Maria, while Fellaini headed hopelessly wide from eight yards.
Five minutes of stoppage time had the nerves jangling around the Etihad, but City closed out a crucial win.
