Bruno Fernandes has been criticised for his performances in big games this season.
That goal turned out to be meaningless as it came from the penalty spot in a 6-1 defeat against Spurs in October.
He fired back in a message to his critics before the City match.
"I don't know what people mean by 'top six', because the teams are in top six in the table," he told Sky Sports, per the Manchester Evening News.
"I score and assist against some of them. I score this season against Tottenham, but people say penalties don't count. So the game against Tottenham doesn’t finish 6-1 but 6-0.
"I'm sure in some moments, I will score, I will assist, and I will perform. And that will help my team-mates to win the game."
He lived up to his comments at the Etihad Stadium as he hit the back of the net after just two minutes.
United were given a penalty when Anthony Martial was felled by Gabriel Jesus in the box.
Fernandes, who has an unbelievable record from the penalty spot, would make no mistake as he put his side ahead.
One man who would have been disappointed to see his effort go past Ederson was Kyle Walker.
The English full-back was named on the bench by Pep Guardiola for the Manchester derby.
But, despite not being on the pitch when Fernandes waited to take his penalty, Walker still tried his hardest to put him off.
Just before Fernandes struck his spot-kick, new footage has emerged which shows the 30-year-old screaming: "He missed it!"
His comment can be heard 0:12 in the below video. Remember to turn your sound up!
The video doesn't make it clear that Walker was the culprit but, according to Evening Standard journalist James Robson, it was indeed him who shouted.
Unfortunately for him, the Portuguese was not to be deterred as he put his side a goal up.
Walker would join the action when he replaced Joao Cancelo in the 65th minute.
But he was unable to transform his side's fortunes as City's 21-game winning streak was snapped.