The tragic woman is said to have cushioned the man’s impact when they landed together on wet ground outside the block of flats in St Petersburg, Russia.
Eyewitnesses told cops they then saw him staggering back upstairs naked to re-join his pals at a party in the building, according to reports.
Police initially thought they were dealing with a brutal sex killing when they found the woman naked from the waist down at the base of the tower.
They also found a TV that appeared to have been thrown from one of the windows above and briefly considered the TV set might have killed the young woman, 5-tv reports.
But this did not explain why she was missing her clothes.
They were then reportedly told the woman and a man were having sex in a ninth-floor flat above before slipping from their window sill perch.
The pair were said to have been at a small but raucous party at the apartment with two other men.
Cops are quoted as saying the woman was killed instantly after landing head first, while the man miraculously only sustained minor injuries.
He has since been tracked down and has been tracked down and quizzed by officers, it was reported.
An investigation is underway.