Hopes of a Boro win evaporated in a 2-0 scoreline for Arsenal at the Riverside Stadium, while United's 3-1 Old Trafford success still leaves the Gunners with that slender but ever-so important one goal difference advantage.
Blackburn made it tough for the Reds, but so many of United's stars are now at the peak of their form that their class eventually told.
Ruud Van Nistelrooy capped another majestic performance with his 38th goal of the season.
Paul Scholes scored another two opportunist goals while Ryan Giggs dribbled and beat opponents with subliminal ease.
Yet, the game turned on a missed penalty two minutes after the interval with United leading 2-1.
Ricardo, replacing injured goalkeeper Fabien Barthez at the start of the second half for his Premiership debut, brought down former United favourite Andy Cole in the United box after he had been put in trouble by Rio Ferdinand's poor header.
David Dunn stepped up to blast the resulting penalty right footed to the Spanish international's right, but Ricardo guessed correctly to beat the ball away.
Thirteen minutes later the points were locked away when a tremendous run through the middle by Giggs ended with him finding Van Nistelrooy unmarked on the left side of the Blackburn box.
The Dutchman took the ball to the by-line before driving a low cross to the near post where Scholes smashed it home from four yards out - his 100th goal for the club.
United had started tentatively and were finally dragged from their lethargy in the 19th minute courtesy of Van Nistelrooy.
David Beckham produced the perfect cross from the right corner of the Rovers penalty area with van Nistelrooy ghosting in on the blindside of Henning Berg to head home from the left corner of the six-yard box.
Rovers were level within six minutes. Barthez failed to cut out Dunn's free-kick from the right and Blackburn's former United defender Berg rose above the home defenders to head across goal and into the far corner of the net from the right corner of the six-yard box.
United's second goal came with four minutes of the first half remaining.
Scholes found Phil Neville galloping down the left. His low cross to the near post was parried by Blackburn goalkeeper Brad Friedel and, after Craig Short failed to clear, Scholes raced in to lash his right-foot shot into the roof of the net from 12 yards.
Friedel made super saves to deny Giggs and van Nistelrooy, while Dunn cleared a Giggs effort off the line, but United could not score another vital goal to cancel out Arsenal's slender goal difference advantage.