Mbappe found Dembele for his second of the game, producing sublime skill by nutmegging Nathaniel Adjei and crossing into the box before doubling his own tally in stoppage time.
Sadio Mane wasted several opportunities but Lallana was clinical, first crossing slickly for Divock Origi to prod home a fine team goal, then side-footing in a pass from the Belgium striker for the third.
London-based group, WSTRN, releases the video to their boarder-crossing single titled "Love Struck", on which they featured the duo of "Tiwa Savage" and "Mr. Eazi".
But stand-in captain Alexander-Arnold quickly made amends, crossing for Wataru Endo who headed home his first Liverpool goal in the 30th minute, before Darwin Nunez blasted in a third to give the Reds a 3-1 lead at half-time.
And within 60 seconds Rashford announced his arrival, turning Bacary Sagna before crossing for Ibrahimovic to shoot over as United made a high-octane start to the second half, pressing and harrying City in an attempt to stop the possession game