Coming hot on the heels of the departure of the iconic Jose Mourinho, this defeat at Old Trafford was like an uncomfortable dream which turned into the worst of nightmares.
They survived a good penalty shout for United after 17 minutes, but then lost John Obi Mikel through a controversial sending-off by referee Mike Dean a quarter of an hour later.
With the game 35 seconds beyond the signalled two minutes of first-half injury time, Chelsea went behind to a Carlos Tevez goal.
Then, seconds from the end of normal time, they suffered from another controversial decision when Tal Ben Haim was adjudged to have brought down Louis Saha in their box and the Frenchman converted the resultant spot-kick.
It was a baptism of fire for new boss Avram Grant, but a magnificent result for United manager Sir Alex Ferguson.
The result, only United's second win in 12 competitive games against the Londoners, put them two points behind league leaders Arsenal.
It was also the first time United had scored more than one goal in a game in 11 matches - an amazing statistic for a side oozing with flare.
United could have had a penalty in the 17th minute when Joe Cole wrapped his right leg around Patrice Evra's ankles as the Frenchman raced into the Chelsea box.
Mr Dean waved play on, but was more pro-active after 32 minutes. Mikel, whose move to Stamford Bridge from Norway was surrounded by controversy after he looked to be heading to Old Trafford went diving in with a tackle on Evra.
The tackle was poor and badly timed, but a booking seemed the most likely punishment and those both on and off the field seemed surprised at Mr Dean's decision.
Ten-man Chelsea held on until the game moved towards the third minute of first-half injury time.
Chelsea failed to clear Ryan Giggs' corner. Wes Brown headed the ball back to Giggs hovering on the right edge of the penalty area and he produced a exquisite left-foot cross to the near post.
Tevez beat Chelsea goalkeeper Petr Cech to the ball and the Argentinian's brave header nestled in the net - his first goal for United since a summer move from West Ham.
If Mikel was unlucky to be sent off, fortune smiled on Joe Cole, who received only a yellow card for his dreadful 74th minute foul on Cristiano Ronaldo.
United's second goal in the final minute came from a penalty award when substitute Saha went over in the Chelsea box after he seemed to make contact with the back of Ben Haim's leg.
But Saha took full advantage of the situation and his straight-driven left-foot spot-kick hit the back of the net with Cech diving to his right.