A homeless predator was busted in the terrifying sex assault of a 19-year-old woman about a block from Gracie Mansion over the weekend, cops said.

Quincy Burks, 30, was lurking around the Upper East Side once again Monday when detectives investigating the sex assault from a few days prior spotted him and arrested him, police sources said. 

He was charged with attempted rape and sexual abuse, according to a criminal complaint.

The disturbing attack occurred around 1:15 a.m. Saturday in the vicinity of East 90th Street and East End Avenue, about a block from the mayor’s official residence.

The teen victim was walking when Burks — who was captured on surveillance footage following her from Carl Schurz Park — threw her to the ground and then assaulted her, according to cops and Manhattan Assistant District Attorney Katelyn Colman.

“The defendant is charged with a brutal sexual assault of a stranger on the sidewalk on the Upper East Side,” Colman said at his Manhattan Criminal Court arraignment Tuesday.

Burks, who had been holding the victim’s hands down, put his hand over her mouth when she started screaming, according to Colman.

The sicko was spooked when a hero doorman rushed to the woman’s aid after hearing her cries for help, police said.

“This young lady was on the floor frantically crying, blood on her shirt and nose,” the doorman, Hector Mateo, recalled.

Mateo — who stayed with the victim until police arrived — said he has a 20-year-old daughter and his “instincts as a father kicked in. I just wanted to help.”

He doesn’t usually work nights, but said his wife told him, “That was really God putting me on the right spot to help somebody else.”

The victim went to New York Presbyterian Cornell Medical Center in stable condition, police said. 

Her alleged attacker — who had only been living in the city for a few months — made his way a couple blocks north to a public storage facility where he accessed his storage locker and changed his clothes, Colman said.

Several hours after the assault, cops released surveillance footage showing the slender and bearded man wearing a white shirt and holding a black umbrella as he casually walked along the sidewalk.

Another clip shows what appears to be the same individual — now wearing a black shirt — sprinting across a crosswalk.

In a third video, the man — previously described by cops as 6 feet tall — stopped on the sidewalk to check his phone and suspiciously checked over his shoulder several times before walking away.

Burks’ attorney, Brett Taylor, argued that cops “may have very well arrested the wrong person” since his client, who he described as a part-time delivery driver living in Brooklyn, is not shown in surveillance videos taking part in the “incident itself.”

He pushed for supervised release, but Judge Pamela A. Goldsmith granted prosecutors’ request to hold Burks without bail.

Burks has no prior arrest history in the Big Apple, cops said. 

But Goldsmith said he has “a very extensive record” in Detroit for assault and baattery, as well as assault with dangerous weapons.

Those arrests are from 2018 and 2022, though it’s unclear if he was ever actually convicted.

Burks is set to reappear in court Friday.