Manchester United 4-2 Manchester City

It was Manchester United's first derby win in five attempts

• Man Utd go four points clear of City

• City have lost six of last eight games

• Aguero scores 100th City goal

Manchester United ended a dismal derby sequence and piled the pressure on Manuel Pellegrini as his Manchester City side were well beaten at Old Trafford.

City, attempting to recover from successive away defeats at Liverpool, Burnley and Crystal Palace, made a blistering start and took an early lead through Sergio Aguero.

It was all downhill from then on for the fading Premier League champions as Ashley Young and the revitalised Marouane Fellaini put United in front before half-time.

Louis van Gaal's side never looked like surrendering the advantage as they secured a sixth straight Premier League win with further goals from Juan Mata and Chris Smalling.

The victory put them four points ahead of City and firmly on course for a return to the Champions League next season.

As for City, this was the sort of capitulation that never reflects well on any manager and Liverpool could narrow the gap to Pellegrini's side to just four points if they beat Newcastle United at Anfield on Monday.

Missing out on the Champions League is the unthinkable scenario for City and Pellegrini, who had won the previous four Manchester derbies - including three at Old Trafford - before his side declined alarmingly after a perfect start.

And to illustrate the turnaround in fortunes, it was only just over a year ago that City's 3-0 win here effectively signalled the end of David Moyes' United reign and put City 15 points ahead of their rivals having played two games fewer.

United are now the team that looks rejuvenated, while City are in serious need of reconstruction as the defensive frailties and fluctuating form that have characterised their season were exposed once more.

City can take solace from having four of their last six games at home but their defence of the title is in ruins and the speculation surrounding Pellegrini will continue, especially if they miss out on the top four.

The Chilean repeated the ploy that worked successfully in that win at Old Trafford last season when a high-tempo start brought a goal inside a minute from Edin Dzeko. It took slightly longer this time but brought the same reward.

David De Gea had already saved an angled shot from Jesus Navas but he was powerless to prevent Aguero converting a simple tap-in from David Silva's pass after intelligent work from James Milner.

United were on the ropes but responded to draw level after 14 minutes. De Gea's long clearance found its way to Ander Herrera and Young reacted first to a rebound after he battled with Gael Clichy to get on the Spanish midfielder's cross.

Young was then the provider as United went ahead after 27 minutes, his cross dropping over Clichy at the far post for Fellaini to head past Hart, who should have kept the effort out having got strong contact on the ball.

City made a change at half-time as injured captain Vincent Kompany, also on a yellow card for a late challenge on Daley Blind, made way for Eliaquim Mangala.

The tide continued to flow United's way and Hart made amends with a crucial double save seven minutes after the restart, first from Wayne Rooney's free-kick then from Michael Carrick as the midfielder looked certain to extend the lead.

City's early zest had disappeared completely and United did get the third goal they deserved after 67 minutes when Rooney's perfect reverse pass released Mata, who beat Hart from a narrow angle.

The visitors felt Mata was marginally offside but once again their defending had been found wanting.

And it turned even uglier for City and Pellegrini seven minutes later when Smalling emerged unmarked through a packed penalty area to glance a header past the exposed Hart from Young's free-kick.

Aguero scored in the closing moments but it cannot count as anything approaching consolation on a dismal day for City but one of pure delight for United.

It was only the third time United have scored more than four goals in a Premier League derby

Wayne Rooney has now assisted 90 goals in the Premier League

Sergio Aguero scored his 100th goal for Manchester City in his 158th game for the club

Ex-Manchester United manager Sir Alex Ferguson watched alongside Simply Red singer Mick Hucknall