Jose Mourinho was humiliated on his return to Chelsea as his former club blew away his Manchester United side at Stamford Bridge.
The Blues, who sacked Mourinho for a second time last year, led after just 30 seconds when Pedro capitalised on slack defending to roll in.
Gary Cahill smashed in the second after United allowed Eden Hazard’s corner to bounce in their box.
United offered little sign of making a comeback, falling further behind when Hazard drilled in a precise 15-yard strike.
N’Golo Kante skipped around a static defence to slot in and seal victory as Chelsea moved within a point of Premier League leaders Manchester City.
The comprehensive win lifted the Blues above Tottenham into fourth, with just one point separating the top five.
United stay seventh as the gap between them and the early pacesetters widens to six points, with almost a quarter of the season gone.
Mourinho was making his first return to Stamford Bridge since he was sacked in December 2015, leaving when the defending champions were 16th in the Premier League.
The Portuguese boss said before the match he was unsure – and also unconcerned – about the reception he would be given by the home fans.
Unsurprisingly, for a man who delivered seven trophies in his two spells at the club, it turned out to be largely positive.
Hundreds gathered to greet Mourinho as he walked off the United team bus, while he received a warm embrace from former skipper John Terry before kick-off.
That is where the Blues’ hospitality ended. Instead, it was his United team who provided the generosity.
And the home fans could not resist a cheeky dig at their former boss – chanting “you’re not special anymore” to the self-proclaimed Special One.
Mourinho said before the game he would not “celebrate like a crazy kid” if his new team scored at Stamford Bridge.
Unfortunately for him, there was little sign of that resolve being put to the test as Chelsea capitalised on his side’s defensive deficiencies.
United were ragged at the back, ripped open by Pedro’s opener without even having a touch and left flapping from then on.
And the severity of the scoreline was emphasised by some startling statistics:
* It was the heaviest defeat for Jose Mourinho in all competitions since Real Madrid’s 5-0 defeat by Barcelona in November 2010.
* United suffered their heaviest Premier League defeat since the 6-1 loss against Manchester City in October 2011.
* The Red Devils lost a Premier League away match by four or more goals for the first time since 1999 – also at Chelsea.
The tone was set when Chris Smalling hesitated in dealing with a long ball, allowing Pedro to nip in and round David de Gea – and United never recovered.
The basic ability to defend a set-piece eluded them for Chelsea’s second, two deflected touches helping the ball on to the unmarked Cahill, who lashed in.
United, without the injured Wayne Rooney, looked unrecognisable from the side that dug in to keep a clean sheet at Anfield on Monday. They looked unrecognisable from any Mourinho side, always expected to be well organised and difficult to break down.
A stony-faced Mourinho watched his static defenders allow Hazard and then Kante to skip into space and score after the break, leaving new Chelsea manager Antonio Conte lapping up the acclaim of a home crowd revelling in their former boss’s misfortune.
“We made incredible defensive mistakes,” said Mourinho. “And then you pay for that.”
Former Italy manager Antonio Conte was tasked with restoring Chelsea’s fortunes after a chastening season, which started under Mourinho’s leadership and ended in the defending champions finishing 10th.
Conte’s start has not been smooth, however.
Back-to-back league defeats against Liverpool and Arsenal last month led to some criticism, forcing him to laugh off rumours of his imminent sacking.
But, after making a tactical switch to a 3-5-2 formation following those defeats, Conte has seen his team flourish.
Three successive victories have pushed the Blues back among the frontrunners, with the Stamford Bridge crowd showing their appreciation for the new manager as he urged them to make more noise during the second half.
“It is important for the manager to find the right solution for your team,” said Conte on his team’s recent revival.
“It was not a good situation when Chelsea conceded in every game – we change and now we are playing good football.”
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