Runaway Premier League leaders Manchester City opened up an eye-watering double-digit lead over rivals Manchester United after Nicolas Otamendi fired Pep Guardiola's men to derby victory.

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.

OLI SCARFF/AFP/Getty Images

---

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.