Not since QPR ran out 4-1 winners at the home of the Red Devils on New Year's Day 1992 have the champions conceded so many on home turf.
Rafa Benitez's men produced a performance on a par with their memorable 4-0 demolition of Real Madrid in midweek to reignite the title race, although Sir Alex Ferguson's men still have a game in hand.
Arsenal are back up to fourth with Aston Villa not playing until Sunday courtesy of a 4-0 home victory over struggling Blackburn, while Everton pushed poor travellers Stoke back into the drop zone and enhanced their European hopes with a 3-1 success at Goodison Park.
Portsmouth were forced to settle for a point against 10-man Middlesbrough at the Riverside after conceding a last-gasp leveller. Hull City and Newcastle similarly shared the spoils at the KC Stadium in a result which does little for either side's hopes of avoiding being sucked into the bottom three.
Fulham claimed a first triumph away from Craven Cottage this season with a 3-1 win over Bolton at the Reebok, as Sunderland slipped back towards the wrong end of the table after going down 2-1 at home to Wigan.
AstonishingLiverpool inflicted Manchester United's heaviest home defeat in 17 years as they reignited their title bid with an astonishing 4-1 success at Old Trafford.
Benitez's men were forced to come from behind after Cristiano Ronaldo fired the Red Devils into the lead from the spot after Jose Reina had needlessly felled Park Ji-sung.
First Nemanja Vidic's dismal defending allowed Fernando Torres to equalise with a smart finish before Steven Gerrard fired the Reds ahead on the stroke of half-time with a penalty after being felled by Patrice Evra.
Vidic's day got even worse when he saw red 14 minutes from time when he hauled down Gerrard as he burst through with Fabio Aurelio curling the resulting free-kick beyond a motionless Edwin van der Sar.
Substitute Andrea Dossena added a late fourth as he latched onto Reina's long clearance to lob the Dutchman with an already sparsely-populated Old Trafford then emptying even more rapidly.
Andrey Arshavin opened his Arsenal account as Arsene Wenger's men climbed back into fourth place courtesy of a 4-0 home success over struggling Blackburn.
Arshavin found the net for the Gunners at the fifth time of asking as he bundled home from close range after Theo Walcott's cut-back from Nicklas Bendtner's probing ball down the right flank, although replays suggested Andre Ooijer may have got the final touch.
But there was no doubts over the Gunners' second as Arshavin picked up possession on the left of the box before tricking his way beyond Danny Simpson and then firing high over Paul Robinson from an impossibly tight angle.
The Russia international then drew a stunning save from Robinson in the closing moments with Emmanuel Eboue gratefully slotting home the rebound.
Eboue then added further gloss to the scoreline from the penalty spot after Martin Olsson had brought down Carlos Vela.
Middlesbrough snatched a last-gasp draw against Portsmouth at the Riverside despite being reduced to 10 men.
Pompey claimed a crucial advantage on the half-hour mark as Glen Johnson collected a short corner and attempted to turn inside, with the ball bouncing up for Peter Crouch to fire home an impressive volley from the edge of the area.
Boro's hopes of getting back into the match were dealt a major blow as Matthew Bates was dismissed 13 minutes from time after receiving a second yellow card from referee Martin Atkinson for diving in the area.
But Marlon King fired home from close range after Pompey failed to deal with a late corner and David James could only parry Tony McMahon's header, and there was still time for Afonso Alves to miss a one-on-one with James
Bottom threeEverton continue to press for European qualification as the pushed Stoke back into the Premier League's bottom three.
Jo continued his goalscoring form since moving to Goodison Park on loan from Manchester City, with goalkeeper Thomas Sorensen at fault as he allowed the striker's shot from Marouane Felliani's pass to squirm under his body.
And Sorensen did little better with the second, palming away Tim Cahill's header from Leon Osman's cross onto the foot of a grateful Joleon Lescott who could not miss from two yards out.
Stoke dragged themselves back into the game after the break as Ryan Shawcross was allowed a free header in the Everton box from Liam Lawrence's corner with the ball dropping just inside Tim Howard's far post.
But Felliani made the game safe at the death as a produced a moment of great control to bring down Leighton Baines' long ball and fire home via the aid of deflection.
Hull City boss Phil Brown claimed before the meeting with Newcastle he would be happy to take a point against their fellow strugglers, and that was exactly what the Tigers did.
Geovanni, whose most recent action at the KC Stadium was a display of petulance after being subbed against Blackburn which earned a stinging rebuke from his manager, headed his side in front after just nine minutes.
The Brazilian fed Craig Fagan down the left flank and he had time and space to pick out his team-mate who had made his way to the far post unimpeded.
But the Magpies were back on terms before the break as Steven Taylor showed a deft touch for a centre-back to guide Nicky Butt's cross over the head of Matt Duke.
Sunderland are far from safe and are glancing nervously over their shoulder after going down 2-1 at home to Wigan.
The Latics took the lead as dismal Sunderland defending allowed Ben Watson time and space to fire home from the edge of the box in the 12th minute after Chris Kirkland's long clearance.
The Black Cats were allowed to equalise as the Latics defence followed suit from their hosts, with Kenwyne Jones eventually heading Marton Fulop's punt into the path of Grant Leadbitter to slot home.
Former Newcastle midfielder Charles N'Zogbia then produced a moment of individual brilliance, running half the length of the field to beat Fulop at his near post, with the home side fuming play had not been stopped due to an injury to Jones.
Fulham claimed their first away win at the 15th time of asking as Bolton were sucked back towards the scrap for survival.
Jussi Jaaskelainen produced a great save from Bobby Zamora's volley from close range to keep Bolton on terms before being undone by a comical piece of defending.
Andy O'Brien intercepted Simon Davies' through-ball but only succeeded in guiding it beyond Jaaskelainen, allowing Andy Johnson to steal in and slide home.
But the home side responded immediately with Kevin Davies chesting the ball into the pass of Mark Davies before receiving possession back and beating Mark Schwarzer with an impressive finish across the Cottagers' keeper.
Fulham were back in front as Simon Davies kept his cool to score despite the efforts of Jlloyd Samuel on the line after Danny Murphy's initial effort had come back off the crossbar.
Diomansy Kamara added a late third as Fulham doubled their paltry tally of away goals for the season at a single stroke.