United need just one more point to seal the title after they claimed a 2-1 win over Chelsea in their huge showdown at Old Trafford.
Javier Hernandez took just 36 seconds to break the deadlock as he seized on a David Luiz error to net his 20th goal of the season.
Skipper Nemanja Vidic headed home a Ryan Giggs cross in the 23rd minute as United deservedly doubled their advantage although Didier Drogba and Salomon Kalou both went close for the visitors before half-time.
Chelsea threatened an unlikely comeback after Frank Lampard's 68th-minute header restored hope but a relieved Sir Alex Ferguson saw his side cling on for a priceless triumph.
The defending champions needed a win to leapfrog United on goal difference but Carlo Ancelotti's men are now six points behind with just two matches remaining.