text: 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.
  Analysis: Why it is too early to write Man Utd off
  Relive how Chelsea ruined Mourinho's return
  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:
  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."
  Chelsea manager Antonio Conte:
  "We made a fantastic start. We scored the early goal but we continued to play good football, intensity and possession, create many chances. Today we didn't concede, which was important. It was a type of win that increases the confidence.
  "We wanted to show our ambition and give the satisfaction to our fans and show last season was very bad."
  Manchester United manager Jose Mourinho:
  "You come with a strategy, you cannot concede a goal in the way we did.
  "We were coming to have an offensive approach. We wanted to create chances; we showed that after the 1-0. The second and the third were counter-attack goals.
  "It is one of those days when you give the advantage to opponents by doing nothing.
  "In terms of points, we got zero points, we lose three points. We are six points from the top, three from the top four, we now need to win matches. We need to win our matches now, which are not easy.
  "We need to win to close that gap - after these last three matches, we made two out of nine. We now need points."
  Next comes the not-so-small matter of midweek derby matches for both teams.
  Chelsea travel across London to face West Ham in the EFL Cup fourth round on Wednesday (19:45 BST), while Manchester United host neighbours City at Old Trafford in the same competition on the same day (20:00 BST).
  Match ends, Chelsea 4, Manchester United 0.
  Second Half ends, Chelsea 4, Manchester United 0.
  Foul by Ander Herrera (Manchester United).
  Nemanja Matic (Chelsea) wins a free kick in the defensive half.
  Corner,  Manchester United. Conceded by Thibaut Courtois.
  Attempt saved. Marcos Rojo (Manchester United) left footed shot from outside the box is saved in the top right corner. Assisted by Ander Herrera.
  Attempt blocked. Zlatan Ibrahimovic (Manchester United) left footed shot from the centre of the box is blocked. Assisted by Marcos Rojo.
  Attempt saved. Nathaniel Chalobah (Chelsea) right footed shot from outside the box is saved in the bottom left corner. Assisted by N'Golo Kanté.
  Offside, Chelsea. Marcos Alonso tries a through ball, but Michy Batshuayi is caught offside.
  Attempt blocked. Victor Moses (Chelsea) left footed shot from the right side of the box is blocked. Assisted by Willian.
  Foul by Antonio Valencia (Manchester United).
  Marcos Alonso (Chelsea) wins a free kick on the left wing.
  Foul by Ander Herrera (Manchester United).
  Nathaniel Chalobah (Chelsea) wins a free kick in the defensive half.
  Foul by Anthony Martial (Manchester United).
  César Azpilicueta (Chelsea) wins a free kick in the defensive half.
  Attempt blocked. Paul Pogba (Manchester United) right footed shot from outside the box is blocked. Assisted by Anthony Martial.
  Foul by Marcos Rojo (Manchester United).
  César Azpilicueta (Chelsea) wins a free kick in the defensive half.
  Antonio Valencia (Manchester United) wins a free kick in the defensive half.
  Foul by Michy Batshuayi (Chelsea).
  Corner,  Manchester United. Conceded by Thibaut Courtois.
  Attempt saved. Zlatan Ibrahimovic (Manchester United) right footed shot from the centre of the box is saved in the bottom right corner. Assisted by Juan Mata.
  Foul by Zlatan Ibrahimovic (Manchester United).
  David Luiz (Chelsea) wins a free kick in the defensive half.
  Substitution, Chelsea. Michy Batshuayi replaces Diego Costa.
  Substitution, Chelsea. Willian replaces Eden Hazard.
  Foul by Anthony Martial (Manchester United).
  Nemanja Matic (Chelsea) wins a free kick in the defensive half.
  Paul Pogba (Manchester United) is shown the yellow card for a bad foul.
  Foul by Paul Pogba (Manchester United).
  Nemanja Matic (Chelsea) wins a free kick in the defensive half.
  Attempt saved. Diego Costa (Chelsea) left footed shot from the left side of the box is saved in the centre of the goal. Assisted by N'Golo Kanté.
  Attempt missed. Zlatan Ibrahimovic (Manchester United) right footed shot from the centre of the box is too high. Assisted by Daley Blind with a cross following a set piece situation.
  Anthony Martial (Manchester United) wins a free kick on the left wing.
  Foul by Victor Moses (Chelsea).
  Attempt missed. Paul Pogba (Manchester United) right footed shot from outside the box misses to the right. Assisted by Anthony Martial.
  Substitution, Chelsea. Nathaniel Chalobah replaces Pedro.
  Goal!  Chelsea 4, Manchester United 0. N'Golo Kanté (Chelsea) right footed shot from the centre of the box to the bottom left corner. Assisted by Pedro.
  Attempt missed. Ander Herrera (Manchester United) left footed shot from outside the box is high and wide to the left.
target: Jose Mourinho was humiliated on his return to Chelsea as his former club blew away his Manchester United side at Stamford Bridge.