Two goals up at the break, through Manuel Ugarte and Diogo Dalot, things were looking plain sailing for Ruben Amorim's Reds.
But Lyon had other ideas and forced extra-time with efforts by Corentin Tolisson and Nicolas Tagliafico. Despite losing skipper Tolisso to a second yellow card, the French side were impressive in the extra-time period.
Rayan Cherki blasted them in front and Alexandre Lacazette converted a penalty to seemingly dump United out.
Yet, somehow, from the depths of despair, Ruben's men dragged ourselves back from the brink as Old Trafford exploded with unbridled passion and joy.