Police Saturday released a sketch of the knife-wielding man who sexually assaulted a woman in her Brooklyn apartment building early Thursday morning.

The attacker pulled a kitchen knife on the victim after trailing her into her building on Evergreen Avenue in Bushwick just after midnight, cops said.

The fiend then pushed the woman to the fourth-floor landing, where he snatched her purse before forcing her to perform a sex act on him, authorities said.

The suspect is believed to be in his mid- to late 20s.

He stands about 6 feet tall and weighs 185 pounds, police said.