The local rivals dominating the national league were ultimately separated by a piece of individual skill by Sergio Aguero, who entered the fray as a substitute after Vincent Kompany's own goal cancelled out James Milner's deflected opener.
Sir Alex acknowledged, "They brought on Aguero who's always a threat and maybe we can look at ourselves for the space we gave him for his goal but nonetheless he is a good finisher."
Kompany's own goal was initially credited to his United counterpart Phil Jones, who forced the issue by meeting Robin van Persie's free-kick delivery to the far post. His involvement in the equaliser capped a fine display by the versatile England defender.
"He was tremendous," praised Sir Alex. "He's a fantastic player, the boy. He's not had a lot of football at centre-back but today he's come in, into a difficult situation when some of the other centre-backs are injured, and, like we expected, he was very good.
"There were some terrific performances tonight – Robin van Persie was fantastic – so there were a lot of pluses in that respect."