Darren Fletcher's first-half header proved enough to wreck Chelsea's 40-match unbeaten record at Old Trafford this afternoon.
After a week from hell, which saw a vicious Roy Keane rant sandwiched either side of miserable defeats to Middlesbrough and Lille, Manchester United staggered off the canvas in amazing fashion.
Fletcher's looping effort enabled the Red Devils to climb into third spot and reduce Chelsea's advantage on them to 10 points.
But, much more than the mathematics, the result will revive hope Alex Ferguson is the man to lead United back to the promised land.
Cristiano Ronaldo emphasised the attacking ambition within the
United ranks when he fired a 30-yard strike over the crossbar within the opening three minutes.
However, Didier Drogba reminded the home side of the task they faced when he reacted to Frank Lampard's pass before seeing Edwin van der Sar save his close range lob five minutes later.
Having played so dismally against Lille in midweek, United had bite in the tackle and a purpose to their attacking play, with Alan Smith and Paul Scholes in particular making life difficult for Chelsea in midfield.
And the home side were rewarded on 31 minutes when Fletcher deservedly put United ahead with a looping far post header.
The Scotland midfielder escaped his marker at the far post to connect with Ronaldo's cross, but his header appeared to be too acute to find the net. However, the ball looped high before dropping into the net at the far post beyond the head of Chelsea captain John Terry.
Buoyed by the goal, United continued to press Chelsea in the second-half and the home side wasted a golden chance to extend their lead on 54 minutes when Ruud van Nistelrooy fired over the crossbar from ten yards.
Wayne Rooney's floated pass had picked out Fletcher inside the penalty area, but the Scot's perfect pass to Van Nistelrooy lacked the finishing touch it deserved.
United couldn't afford to be so wasteful against a team of Chelsea's attacking threat and Drogba and Lampard both gave the home side worrying moments as the champions went in search of an equaliser.
Chelsea's onslaught continued and Lampard and Asier del Horno both went agonisingly close to equalising as United were pushed further and further back.
Lampard was brilliantly denied van der Sar from close range on 68 minutes after good work by Drogba and full-back Del Horno then volleyed over the crossbar from six yards after racing onto Duff's cross.
Substitute Shaun Wright-Phillips then forced van der Sar into another fine save with a low strike from 25 yards, but United held out to seal a dramatic victory.
