box and Mohammed Abdellaoue opted to line up an outrageous back-heel flick which nestled inside De Gea's post.
The Reds' riposte was swift. Nani's surging run was clumsily halted, 25 yards from goal, giving Rooney the perfect opportunity to whip a wonderful free-kick over the Hannover wall and inside the static Zieler's post.
Both Anderson and Antonio Valencia were introduced in place of Vidic and Chicharito, and the Brazilian midfielder threaded a neat through-ball to tee up United's leveller. Rooney latched onto the pass, rounded Zieler and tumbled after contact from the former United stopper.
Despite missing a spot-kick against Barcelona earlier this week, the England striker confidently sent Zieler the wrong way from 12 yards - and United weren't done there. With growing zip and dander about their play, the visitors incredibly moved ahead with six minutes remaining.
Nani's clipped diagonal cross found Rooney behind the Hannover defence, and his alert downward header gave Kagawa an opening - albeit at a diminishing angle - and the Japanese play-maker drilled a right-footed effort across Zieler and into the far corner.
Nani almost notched a fifth goal when a clearance thudded against his shoulder and dribbled wide, then he chipped wide of Zieler's goal after being put clean through, but a happy ending to the DHL tour had already been assured.
Hannover 96: Zieler; Chahed (Cherundolo 46), Avevor, Eggimann (Haggui 46), Pander (Giesselmann 86); Nikci (Stindl 46), Hauger (Schmeidebach 46), Andreassen (Pinto 46), Rausch (Hustzi 46); Sobiech (Abdellaoue 46), Schlaudraff (Ya Konan 46).