Karan Dutt and Akash Kumar fell 40 feet below on the ground after the motorcycle they were riding hit a side wall on the incomplete flyover around 7.30 am.
Mr Dutt was brought dead to the hospital, his friend Akash Kumar has suffered multiple critical injuries.
Both had gone for a joyride and lost balance over a flyover bend due to overspeeding, Deputy Commissioner of Police Aslam Khan said.
The residents in the area however claimed that both were performing stunts on the motorcycle when it crashed through the flyover's side wall and fell off amid poor visibility in morning hours.
Area residents said motorcycle riders often visit the incomplete flyover and perform stunts since Public Works Department officials have neither barricaded it nor deployed any guard.
A case of rash driving on a public way, causing hurt by acts endangering life and causing death by negligence has been registered, Mr Khan said.