The incident happened at 3:25 a.m. on Saturday in the 200 block of Landover Road in the Bryn Mawr section of Radnor Township.
Police say the female victim said she heard knocking and, believing it was her roommate, opened her bedroom door.
That's when the she was knocked down by an unknown man, described as a black male wearing nothing below the waist.
The man and the victim struggled on the floor. After struggling and screaming, police say the attacker fled the home on foot.
The man is believed to have run toward the Wawa store at 201 Bryn Mawr Avenue, still naked below the waist.
The suspect was only wearing a grey t-shirt and a piece of red clothing over his face.
Anyone with information is asked to call Radnor Police Investigations Unit at 610-688-0503.
