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.