Having travelled to Philadelphia with an 11-match winless streak in tow, Jason Kreis will have wanted his side - in their inaugural season as an MLS outfit - to enjoy a fast start.
Unperturbed, City carried on in the same vein and ex-Barcelona hitman Villa missed two fine chances to open the scoring - the first of which was saved by Brian Sylvestre.
Their breakthrough came within a minute of the restart, as CJ Sapong netted his fourth goal of the season by converting Le Toux's teasing cross.
Philadelphia's advantage lasted less than six minutes, however, as Thomas McNamara's effort from outside the box left Sylvestre with no chance.
Both sides looked poised to share the spoils, but second-half substitute Mullins came off the bench to snatch the win with three minutes remaining as City secured their second victory as an MLS club. body check tags ::