The sickening attack was caught on surveillance video released by authorities on Saturday.
According to police, the suspect followed the 51-year-old victim into an elevator in an apartment building on 108th Street and 62nd Drive in Forest Hills just after noon on Friday.
The suspect exited the elevator before reentering again shortly afterward, displaying a knife and demanding money from the victim.
The victim dumped the contents of her purse on the floor, and the suspect then searched her body for any additional property.
Authorities say that's when the suspect pulled down her pants and began sexually assaulting her.
The victim managed to push the suspect out of the elevator, where he ran to a stairwell and fled the building.
The victim was taken to a nearby hospital for medical evaluation and is said to be in stable condition.
The suspect is described as a medium-complexion man, bald, heavy-set, between 55 and 60 years old, standing roughly 6'0" tall and was last seen wearing a black hooded sweatshirt, black pants, black sneakers, and a multicolored gaiter.
Anyone with information in regard to this incident is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782). The public can also submit their tips by logging onto the CrimeStoppers website at https://crimestoppers.nypdonline.org/ or on Twitter @NYPDTips.
Police say all calls are strictly confidential.