United survived an early scare to take all three points at Old Trafford with a 4-1 victory over Blackburn Rovers.
In a pulsating affair, second-half goals from Paul Scholes, Michael Carrick, Ji-sung Park and substitute Ole Gunnar Solskjaer cancelled out Blackburn's 29th-minute opener to strengthen United's lead at the top of the Premiership.
Watched by a record Premiership crowd of 76,098, the final score flattered United somewhat after a frustrating first-half display that saw the Reds lose Nemanja Vidic with a broken collarbone and go into the change-rooms a goal down.
Sir Alex made three changes to the United team that beat Middlesbrough in the FA Cup 12 days ago. Kieran Richardson made way for Ji-sung Park, while Paul Scholes returned from a three-match suspension to partner Michael Carrick in the centre of midfield. In goal, Edwin van der Sar started his first match since picking up a calf injury three weeks ago and needed to be alert early as David Dunn flashed a shot narrowly over the bar.
The Reds soon settled but found it difficult to create clear chances against a Blackburn defence well marshalled by captain Ryan Nelson. Ronaldo shot just wide of Brad Friedel's right-hand post inside 10 minutes before Wes Brown and Michael Carrick combined to mop up in the Reds' area.