Sir Alex Ferguson's side had to wait until the final 10 minutes to get the three points, as the home side frustrated them for long stretches before good strikes settled the match
The reigning champions dominated for long periods of the game, but had to wait until the last 10 minutes to score as Valencia hit a ferocious effort into the far corner from the wing, while Young hit another good superb shot from distance on the spin with five minutes remaining.
Sir Alex Ferguson made three changes to the side who beat Fulham 1-0 last Monday, with Chicharito, Paul Scholes and Phil Jones replacing Ryan Giggs, Danny Welbeck and Ashley Young.
Steve Kean, meanwhile, only made one alteration to the team who lost to Bolton last weekend, with Mauro Formica dropping to the bench and Bradley Orr coming in to replace him.
||Blackburn are now 6/4 with William Hill to be relegated from the Premier League.
United started much the brighter side, with Chicharito coming close on a few occasions in the opening 15 minutes.
The striker was looked dangerous on the shoulder of the last defender, ably assisted by some fine early passing from Antonio Valencia, Wayne Rooney and Michael Carrick.
His first opportunity came when Rooney found him via some shaky defending, but the striker's effort was an early swipe that flew wide.
His next effort came mightily close to finding the back of the net, getting on the end of Valencia's cross at the front post that Paul Robinson did brilliantly to get a hand to. The ball bounced onto the post and back onto the keeper, but he managed to turn and snaffle it up before it crossed the line.
Carrick then went on a rare stroll forward, but his effort from distance flew over Robinson's goal.
Fairly soon afterwards, David de Gea was given his first task of the night, making a leaping save to his left to stop Junior Hoilett's effort from 25-yards.
Jonny Evans was the next player to put in an effort on goal, placing a low effort at goal after a corner, but Robinson dealt easily with a simple save to his left.
Former Blackburn man Phil Jones could only head wide when unmarked minutes later following a great sweeping move involving Patrice Evra, Scholes and Valencia.
United then had claims for a penalty turned down as a Carrick cross was charged down by Scott Dann. The ball hit the defender on the elbow, but he had it tucked in towards his body.
De Gea then came to the rescue twice more before half-time for United. A long throw was not quite dealt with by the Spanish keeper, punching to the edge of the box, and as Evra failed to clear it, Marcus Olsson fired in a fierce half-volley that he tipped over very well.
From the resulting corner, the young keeper did very well to reach Grant Hanley's header as it threatened to loop in.
United came out after half-time on the front foot, putting in some dangerous crosses and Rooney hitting a venomous effort wide from distance.
Ten minutes into the second-half, Rooney had another opportunity from distance, this time from a free-kick after Scholes was caught with an elbow in a tackle by Hanley.
The striker whipped in his effort but Robinson got across to palm it wide. Rafael then had a long-range shot well-saved, and the pressure from the visitors had Blackburn on the ropes.
But Yakubu then had two efforts in a minute following some sloppy play from Carrick, but he wasn't punished as both shots flew off target.
Morten Gamst Pedersen then tested De Gea from a free-kick as his wall proved ineffective, with the keeper just about stopping the ball as Rio Ferdinand came in to sweep up the danger.
Pedersen then had the ball in the net with a great strike from the edge of the area, but the ball had already gone out of play as Steven Nzonzi took on Evans in the corner.
Sir Alex then looked to his substitutes with Giggs replacing Jones and Welbeck coming on for Chicharito as United went for a more orthodox 4-4-2 formation.
United were starting to apply serious pressure as the game entered the final 20 mintues, but with just over 10 to go, Rio Ferdinand made a fantastic tackle to prevent Yakubu from getting on the end of a cross and turning the ball past De Gea.
But in the 81st minute, United finally got the goal that their pressure deserved, through the man many claim to have been their best performer this season.
Valencia received the ball wide on the right, taking on his defender before slamming an effort across the face of goal and into the far corner.
If the winger had meant it, it would be an unbelievable strike, although questions will be asked how Robinson allowed the effort past him.
And in the 86th minute United made sure of the points, as substitute Young received the ball with his back to goal on the edge of the area, before spinning and whipping a powerful effort past Robinson, who had no chance as the curl on the ball took it from outside the post into the bottom corner.
The rest of the game was played out with Blackburn attempting to find a goal, but coming up against a solid defence as United held on to secure the three points that took them five clear at the top.