Chelsea hit eight past hapless Aston Villa
Chelsea striker Fernando Torres began the goal glut after three minutes at Stamford Bridge and David Luiz and Branislav Ivanovic made it 3-0 at the break.
Frank Lampard marked his 500th Premier League game and first league start since October with a rasping fourth before Ramires (two), Oscar and Eden Hazard joined the fun as Chelsea, who also missed a penalty, secured a first home league win under interim manager Rafael Benitez to move up to third.
United, who led at Swansea through Patrice Evra before being pegged back by league top-scorer Michu's 13th goal this season, hold a four-point advantage over Manchester City, who beat Reading 1-0 on Saturday, heading into a busy holiday programme.
They have 43 points from 18 games, followed by City on 39 and Chelsea, with a game in hand, on 32.
"As a team we had the balance we are looking for," Benitez, whose arrival to replace the sacked Roberto Di Matteo last month was opposed by many Chelsea fans, told Sky Sports.
Chelsea have produced a mixed-bag so far under the Spaniard, with a haul of eight points in his five league games in charge.
England midfielder Lampard, the subject of continued media speculation that he will be allowed to leave at the end of the season when his contract expires, said Chelsea were enjoying playing again.
"I think we showed a great appetite. The early goal helped," said the 34-year-old, who became Chelsea's record top-flight league scorer with 130 goals.
The Villa rout took Chelsea's goal tally to 13 in two games after they thrashed Championship side Leeds United 5-1 to reach the League Cup semi-finals in midweek.
Sunday's victory matched Chelsea's 8-0 demolition of Wigan Athletic at home in 2010. The record Premier League winning margin is Manchester United's 9-0 defeat of Ipswich Town in 1995.
United manager Sir Alex Ferguson was hardly in festive mood after their Wales trip, ruing two points that got away, saying striker Robin van Persie "could have been killed" by Swansea captain Ashley Williams and criticising referee Michael Oliver.
"We absolutely battered them and we are very unlucky," Ferguson said. "It should have been a six-point gap [over Manchester City] today and that is the disappointment."
Ferguson was incensed when a prone Van Persie was struck in the head from point-blank range by a clearance from Williams with the whistle having been blown for a foul on the Dutchman.
The Scot said it was a "deliberate act" and called for Williams, booked along with Van Persie, who escaped injury, in the melee that followed, to receive a long ban.
"Robin van Persie is lucky to be alive. It was a disgraceful act from their player today and he should be banned by the FA. Robin could have had a broken neck," said a seething Ferguson.
United, welcoming back Serbia defender Nemanja Vidic for his first start since September, went ahead when France international Evra met Van Persie's corner with a glancing header.