Tane Tu'ipolutu scored the winning try in added time as Newcastle snatched a dramatic 21-20 victory over Harlequins to reach the LV= Cup final.
The Falcons had trailed 13-3 during a first half dominated by Harlequins before man of the match Jimmy Gopperth inspired a comeback after the interval.
The New Zealand fly-half guided Newcastle into the lead with a breakaway try and three penalties only for Harlequins to hit back in a see-saw encounter with a try from full-back Mike Brown.
Rory Clegg's touchline conversion with nine minutes remaining seemed to have put the game safe for Harlequins - but Newcastle were not done yet.
With time up on the clock, Gopperth and Alex Tait combined to send Tu'ipolutu over in the corner and seal Newcastle their first cup final appearance since they won the Powergen Cup in 2004.
The Falcons will meet either Gloucester or the Newport Gwent Dragons at Franklin's Gardens on March 20.