Manchester United boss Jose Mourinho insists they had Manchester City rattled at 2-1.
Eventually Ilkay Gundogan took the game away from United with City's third goal.
But Mourinho said: "Everybody changed after the penalty. Even Pep [Guardiola], even them.
"They felt it then and they became a counter-attack team. They have the power to do that. They bring [Leroy] Sane on and put [Raheem] Sterling in the front. They put [Ilkay] Gundogan in the middle of the park to give them more consistency and fresh legs. They have the team to do that, but everybody felt it."