The teenager was a surprise inclusion in Louis van Gaal's side to face FC Midtjylland, but it didn't take long before he'd repaid the Dutchman's faith.
The youngster found the back of the net twice and became United's youngest ever goalscorer in European competition.
The Red Devils' long affinity with academy products made that night all the more special.
In fact, one of Rashford's teammates at youth level who was in the crowd has since gone on to make a name for himself in the first team: Dean Henderson.
There is currently uncertainty surrounding Henderson's future as he battles with David de Gea for the number one shirt.
The 'keeper more than showed during his loan spell at Sheffield United that he's capable of playing week in, week out in the Premier League.
Many United fans would like to see him picked by Ole Gunnar Solskjaer more regularly - not only because of De Gea's countless errors, but because of his history at United.
The club have shared a clip of him celebrating with Rashford that night in 2016. Some will have thought it was a random member of the crowd, but the duo have been reminiscing about that remarkable moment.
“You were in the crowd,” Rashford recalled to Henderson on United's official website.
“The Academy get particular seats and they'd just moved you. They used to be high up, the tickets, but not long after I started training with the first team the seats moved to the Family Stand.
“I just knew that there were people there and as I was running I just saw you and you grabbed me! Great memories. That’s probably the bit I remember the most. I remember the goals and stuff and how they happened, but other than that I don’t really remember the game itself. I just remember certain moments.”
“Growing up with you for the last few years and seeing you come onto the pitch was just great.
“I had a huge amount of pride seeing you on there and when the ball fell to you and you hit it, I was just buzzing. And for the second goal you ran straight to the same place; it was fantastic. We spoke about it the next day and I was still buzzing and I wanted to know what it was like to play out there.”News Now - Sport News