Manchester United's Wayne Rooney, top, vies for the ball with Blackburn's Jason Lowe during their Premier League match at Ewood Park Stadium, Blackburn. (AP Photo/Jon Super)
With seven rounds left, United is clear of crosstown rival Manchester City and favourite to win its 20th league title.
Valencia cut in from the right wing and fired a swerving shot from a tight angle that flew past goalkeeper Paul Robinson and into the far corner in the 81st minute. Young made sure of the win with a low shot in the 86th.
Blackburn, which dropped into the relegation places on goal difference, had a goal disallowed when Morten Gamst Pedersen's 63rd-minute shot was ruled out because the ball went out of play in the buildup.
