The champions had kept up their free-scoring ways, going three goals up by half-time thanks to Chris Smalling, Nani and Wayne Rooney but the final scoreline did not reflect a game where visitors Chelsea had 21 attempts at goal.
The most awful miss came from Fernando Torres, who inexplicably shot wide in front of an open goal in the 83rd minute, somehow managing to eclipse Rooney's own howler earlier when the United striker had slipped while taking a penalty.
As Old Trafford erupted into a loud chuckle at Torres' misfortune, the beleaguered Spaniard fell to his knees unable to believe what had happened on a day where he had otherwise shown glimpses of his best and had netted his first goal of the season.
"Two of the best strikers missed crazy opportunities," Chelsea boss Andre Villas-Boas told a news conference. "It was a chaotic game."
United, who have won five games out of five, took just eight minutes to go ahead when Smalling headed in an Ashley Young free-kick from the left but looked offside.
They doubled the score when Nani conjured a chance out of nothing, netting a scorcher from 25 metres out on 37 minutes after an excellent ball across the pitch from Jonny Evans.
The winger celebrated with a cartwheel and from then on United were free-wheeling as Rooney added a third on the stroke of half-time after the ball fell kindly as United took their chances while the visitors did not.
Chelsea, who had missed gilt-edged opportunities through Ramires and Torres, came out after the break knowing they needed to do something different and introduced forward Nicolas Anelka for midfielder Frank Lampard.
The substitution paid immediate dividends as the Frenchman put Torres through for a great finish with a flick of his foot as he notched just his second goal for the London club since his record 50 million pound move in January.
CARELESS MISTAKES
Torres had several opportunities as he suggested he was looking more like the player who had sparkled in his Liverpool days and not just because he had ditched his brunette locks in favour of a return to blonde.
He looked hungry going forward and twisted and turned to get himself into the right places in the box with just his final touch letting him down as he kept shooting wide and over.
Just how he managed to put the ball several metres wide when he had done all the hard work to get through the United defence and past keeper David de Gea will haunt him for some time as a chance he could have scored in his sleep.
Villas-Boas said he was delighted with the way his players had kept pushing after the "negative impact" of the half-time scoreline but it was counterpart Sir Alex Ferguson who had the most to be happy about as United went two points clear at the top.
But the careless mistakes, such as Anderson passing straight to Chelsea players several times, stuck in his mind.
"We gave the ball away so many times and they kept counter attacking and they could have scored two or th
