Joao Plata Cotera did manage to work MacMath, who was equal to his effort from a tightening angle.
The hosts managed to get themselves back on level terms through Luis Gil, who headed home Morales's cross in the 75th minute.
However, Casey restored the visitors' lead seconds later.
As the clock ticked down it looked like it would be a memorable victory for John Hackworth's men, but Raymon Gaddis handled inside the area and the referee pointed to the spot deep in injury time.
Morales made no mistake from 12 yards out to rescue a point for his team.
The result sees the home side extend their lead at the top of the Western Conference to four points, while Philadelphia are level on points with Sporting Kansas City in the Eastern Conference.