Ronaldinho headed home the winner for the Rossoneri, who did not impress the 'Special One'.
Mourinho snapped: "Milan scored a goal and we didn't, that is the story of this match. They had a few shots on goal and despite playing a man down, we had some great chances.
"I saw two teams tonight and neither one deserved a win more than the other. I will not talk about the goal or the red card, as I don't want to get suspended."
Nicolas Burdisso saw red in the second half, when Ronaldinho's header had already opened the scoring, but Adriano almost snatched an equaliser in stoppages after he came off the bench along with Julio Cruz.
"When I don't like the result, I am not afraid to run risks. I did the same when we were 0-0 against Lecce, but here when we went down to 10 men I couldn't replace Esteban Cambiasso with Mario Balotelli.
"We needed the midfield held together and the way things were going Patrick Vieira would've got a second booking too."
He continued: "A team that plays against Milan, who are basically all midfielders, need to balance things out. We only had two midfielders - Cambiasso and Vieira - so Cruz is in better physical shape and I put him there to put pressure on Clarence Seedorf.
"A side with 10 men that ends the game like this on the attack and forcing Milan to introduce a defender for a forward says it all. Milan were more pragmatic, this is football.
"It seemed a real derby to me and a very entertaining game. I feel 1-1 was the right result, but this was down to pragmatism. It's better to lose a game than to be afraid of playing football. We played."