Rovers' attitude bore no relation to their relegation haunted position as they went at United from the start.
They could point to a possible second-half penalty that never was, although United could feel hard done by over a disallowed goal at the end of the first period.
But United's galaxy of stars means that someone always seems to shine and this time it was Cristiano Ronaldo who came to the fore.
It was his majestic free-kick on the hour which settled the issue, although there were some nervous moments after that.
Record-breaking goalkeeper Edwin van der Sar was rested for the game, being replaced by Poland international Tomasz Kuszczak, who was far from convincing.
United chipped away at Blackburn, until a howling defensive error led to the opening goal after 23 minutes.
Nani's hopeful ball into the Blackburn box should have easily been cut out by Ryan Nelsen, but the New Zealander, with Wayne Rooney on his shoulder, failed to clear.
Rooney, starting his first game for over five weeks, pounced on the mistake to jab in his right-foot shot from eight yards.
In the 32nd minute, it was United's turn to play comic book defending.
Paul Scholes' short pass to Nani was met by an equally sloppy approach from the Portuguese winger when he was easily robbed by Andre Ooijer 50 yards out.
Ooijer's measured pass sent Roque Santa Cruz racing through the middle with Rio Ferdinand in attendance.
As Kuszczak raced off his line, he collided with Ferdinand and Santa Cruz was left with the easy task of netting with a right-foot shot from the right corner of the six-yard box.
It was the first league goal conceded by United since Arsenal's second by Sami Nasri at the Emirates Stadium last November,
United's disallowed goal came in first-half injury time. Jonny Evans rose above Nelsen to head home Nani's corner, only to see referee Howard Webb disallow the effort for an alleged push by Ronaldo on Gael Givet.
The home defence was again found wanting in the 58th minute.
Nelsen, free on the left side of the united penalty area, hit the post with his shot from 12 yards and it took two attempts by Kuszczak to keep out El Hadji Diouf's follow-up effort.
However, two minutes later United were back in front.
Patrice Evra was fouled on the left corner of the Blackburn box and Ronaldo stepped up to send his right-foot free-kick rocketing into the top far corner of the net.
Blackburn's appeals for a penalty were turned down by Mr Webb seven minutes later, after Morten Gamst Pedersen went down in the United box following a clumsy challenge by Rafael.