The convincing win at Old Trafford gave United 64 points while champions Arsenal, who play Everton at Highbury on Sunday after two consecutive defeats, have 63.
Newcastle United kept their title challenge on track by romping to a 5-1 win over Blackburn Rovers at St James Park to stay third but move on to 61 points.
Chelsea consolidated fourth place, which means a place in the Champions League qualifiers, with a 5-0 demolition of Manchester City at Stamford Bridge, where the visitors' Chinese defender Sun Jihai was red-carded in the last minute.
Southampton drew 2-2 with Aston Villa, Charlton Athletic finished 1-1 at Middlesbrough while Sunderland and West Bromwich Albion, respectively bottom and second-from-bottom, were both beaten and now look destined for the first division.
Sunderland lost 2-0 to a West Ham United side who moved out of the bottom three for the first time since early November, while Birmingham City eased their own relegation fears with 1-0 win over West Brom in the Midlands derby.
