A month ago Marcus Rashford was playing for United's under 21s against City's EDS at the Etihad Stadium.
He played on the left that day but the 18-year-old is already central to Louis van Gaal's plans for the remainder of the season.
He roasted Martin Demichelis for the goal and should have had a penalty just before half-time.
More than that, his work rate was incredible.
Out on his feet and struggling with cramp, only he will know where he found the energy to sprint into the corner to hold the ball up in the final minute.
It's easy to forget that this is Jesse Lingard's first full season in the senior side but Van Gaal trusted him to play a key role at the Etihad, picking him as the no.10 ahead of Juan Mata.
His ability to find space and nullify the dangerous Fernandinho when City had the ball were the main reasons United had such a good first half.
Switched to the right in the second half, he was almost playing as a right back for the final 10 minutes as United had to stand strong, but even that didn't bother him.
As it stands, Michael Carrick can leave Old Trafford for nothing in the summer. He's not had his best season- it's not surprising when he's pushing 35- but he showed against City that he deserved a new deal.
He can't play every game any more but he's still a big match player.
His passing was good and his awareness of the danger was vital in the second half.
At one stage he instinctively dropped into the back four to cover after Daley Blind had chased the ball into midfield.
His experience is still vital.
United were good but Marcos Rojo had a bad day at the office.
He lost Jesus Navas in the first 10 seconds and never seemed to recover against the raw pace of the Spanish winger.
He was lucky not to come off at half time after 45 minutes of giving the ball away and gifting Navas another chance to flash the ball across goal.
He was eventually hooked early in the second half and replaced with Antonio Valencia as Matteo Darmian moved to the left.
Luke Shaw can't come back quickly enough.
Louis van Gaal took a lot of stick for his substitutions against Liverpool on Thursday but he got his decisions right against City.
He recognised that Rojo was struggling against Navas and then introduced Bastian Schweinsteiger to tighten up the midfield when City were threatening to overrun us.
He was also quick to take off Matteo Darmian after he moved to the left.
The Italian was struggling with cramp and the fresh legs helped United to see out the last 20 minutes.
Even though it was frantic, we were never really in trouble.