The Portuguese playmaker was substituted during stoppage time of the 2-0 triumph, which ended City's run of 21 wins in all competitions.
But instead of heading to the seats at the Etihad, Fernandes stopped and intently watched the game going on over Ole Gunnar Solskjaer's shoulder.
The 26-year-old put United into the lead early against City as he stepped up to score a penalty won by Anthony Martial.
But Bruno was just as charged-up on the sidelines as he was on the pitch.
Afterwards, the United midfielder gave an impressive post-match speech in which he explained to Sky Sports: "It's not about winning against City, it's about winning every game."
Manchester United fans have loved what they've seen of the midfielder, as he's piled up the goals and assists since his January 2020 move from Sporting CP.
But now United fans are speculating that he might just be a future Man United manager in waiting.
The other goal in United's win over City came just after half-time when left-back Luke Shaw received the ball inside his own half and raced forwards - leaving Man City players in his wake - then exchanged a one-two with Marcus Rashford.
The ball briefly looked stuck under Shaw's feet, but he got it free then sent a pinpoint shot inside the far past.
Manchester City were the favourites going into the Premier League match, as Pep Guardiola's side had won an incredible 21 games in a row across all competitions.
However Man United got out of the traps fast in both halves of the game and could have had more than a 2-0 lead after an hour, had the otherwise impressive Anthony Martial been more clinical.
United are now unbeaten in their last 22 away games.
The victory put Man United up to second in the Premier League table, 11 points behind their local rivals with both teams having 10 games to play.
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