The much-anticipated 175th Manchester derby was comfortably the biggest game of the Premier League season, such was the need for Jose Mourinho's Reds to claw back their swashbuckling rivals.

But the gap between table-topping City and second-placed United grew to 11 points on Sunday as City triumphed 2-1 at Old Trafford, where Otamendi volleyed home a second-half winner after Marcus Rashford had cancelled out David Silva's opener.

The untimely end to United's club record-equalling 40-match unbeaten home run strengthens their rivals' grip on the title after just 16 matches - of which they have won the last 14 in a row.

That is a new top-flight record run within the same season and an outcome that looked likely after Silva gave City a deserved first-half lead, with the playmaker capitalising on a corner that had deflected off Romelu Lukaku.

United fortuitously went into the break level after Rashford capitalised on a Fabian Delph mistake, but the blue half of the city were not to be denied as Lukaku's hashed clearance allowed Otamendi to volley home early in the second half.

Ander Herrera was booked for diving in the box and Ederson Moraes produced an outstanding double save as the hosts tried to snatch a draw, but City move onto 46 points as a result of a victory that leaves Mourinho's men reeling.

The Portuguese had hoped to frustrate Guardiola's men and catch them on the break in the opening period.

The first half of that plan worked initially as last-ditch challenges and David De Gea's sturdy presence frustrated City, who claimed a penalty as Gabriel Jesus went down in the box. Referee Michael Oliver waved away the appeal but did not book the Brazilian despite appearing to take a tumble.

However, United were not creating anything near enough attacking-wise. City fans began to chant "park the bus, park the bus, Man United" and pockets of the home support even chanted "attack, attack, attack" in the first half.

It took a break in play for the opening period to come alive, with Marcos Rojo and Silva both surprisingly able to continue after a sickening clash of heads.

Not long after play resumed, the latter made his mark.

De Gea acrobatically tipped over a fizzing Leroy Sane attempt, but the resulting corner deflected off Lukaku as he challenged Otamendi and Silva rifled home the loose ball.

The away fans went wild and the 43rd-minute opener belatedly jolted the hosts into life.

United's first shot of the afternoon came in stoppage time as Anthony Martial tried his luck against Ederson, who would be beaten.

A raking diagonal ball from Rojo was not dealt with by Delph and Rashford raced in to strike home.

Jesse Lingard was just unable to get on the end of a Rashford cross as United emerged from the break brighter, yet they fell behind again in the 54th minute.

Lukaku could only meet Silva's free-kick to the far post with a hashed clearance that fell kindly for Otamendi to volley home.

It was a gut-punch United struggled to rally from as Ilkay Gundogan's cutback threatened to bring a third.

De Gea superbly denied Kevin De Bruyne but it was United having the lion's share of chances, with Lukaku and Rashford having attempts before Herrera was booked for diving in the box under pressure from Otamendi.

The home side did not give up and only Ederson came to the rescue in the closing stages.

Martial's low cross was met by a first-time Lukaku shot that the City goalkeeper saved from close-range. Quick to his feet, he then denied Juan Mata's follow-up.

Sane was denied by De Gea in stoppage time and the Football Association may have something to say about the smoke bomb from the home support that was too close to Bernardo Silva for comfort.

The full-time whistle brought wild celebrations from all connected to City.