That mistake came from Mile Svilar, who made history in the match by becoming youngest-ever goalkeeper at 18 years and 52 days but saw his costly error - a positional mistake that saw him drift across the line and into the goal with the ball in his hands - hand Marcus Rashford a goal and Manchester United the match.
It was a tough break for the teenager, who was visibly upset after the match.
And that's where fellow Belgian Romelu Lukaku stepped up and showed the type of sportsmanship rarely seen at the top of the game.
The Manchester United star took the time post game to have a word with his young countryman, and while we can't tell you exactly what was said, he message was clearly a positive one.
Lukaku closed the exchange with a hearty hug for the young man.
Great sportsmanship from the Man Utd players this 👏 pic.twitter.com/5aPKICyJ0D— BT Sport Football (@btsportfootball) October 18, 2017
Our readers across the UK can check out the video above.
All class from Romelu Lukaku. https://t.co/GT3x8iD75Z— FOX Soccer (@FOXSoccer) October 18, 2017
And for our U.S. audience, you can see exchange in this clip.