Kagawa received a clattering challenge from keeper Leno when bidding to extend the advantage in the second half before Nani fired wide after a swift interchange of passes with the alert Rooney. Reinartz headed against the woodwork with Rooney grounded and appealing for a foul from a corner but it proved a rare scare with Rooney unlucky to bend a drive wide after knocking the ball through Simon Rolfes' legs.
The points were sealed on 65 minutes when Giggs' corner was headed on by Evra for Rooney to force a sprawling save out of Leno. Evans reacted quickest to the rebound to smuggle the ball in for a third. There was no let-up from David Moyes' side and lofted passes by Kagawa and Rooney led to Smalling getting in on the act by netting from close range.
It always looked like getting worse for Leverkusen but Leno dived to pull off a one-handed stop to thwart Jones and substitute Anderson was unable to finish off Nani's inviting pass. A fifth goal did arrive two minutes from the end when Giggs' through ball was chested past Leno by Nani and the Portuguese winger produced an exquisite finish with the outside of his right foot, jabbing the ball in from an acute angle.
David De Gea was given a chance to show his class when denying Eren Derdiyok. United need a point against Shakhtar Donetsk in the final Group A game to qualify in first place. Following this result, confidence will surely be sky-high for the Reds.