David Moyes' men made a disappointing start and fell behind when David De Gea was unable to keep out Ashley Westwood's powerful free-kick on 13 minutes. Yet Juan Mata and Shinji Kagawa switched positions regularly to good effect and both were involved in the move that led to the equaliser as Rooney expertly headed past Brad Guzan.
Rooney was on the scoresheet again with an emphatically-taken penalty just before the interval, after Leandro Bacuna chopped down Mata as he dragged the ball back inside the area. Christian Benteke missed a sitter when miskicking and allowing substitute Michael Carrick, on at centre-back, to clear. The muscular striker also headed over a Marc Albrighton cross moments later.
However, Alex Büttner's brave header led to Marouane Fellaini supplying a touch inside the area and the ball broke to Mata, who calmly found the net in front of the Stretford End for United's third. Guzan thwarted substitute Adnan Januzaj and Rooney, with Benteke and Aleksandar Tonev unable to convert openings for the Midlanders.
With time running out, the lively Januzaj crossed for fellow sub Hernandez to poke home a fourth as the Reds warmed up nicely for Bayern Munich on Tuesday.