St Mirren came from behind to beat Welsh Premier League champions The New Saints and book a Scottish Challenge Cup final date with Dundee United.
Ryan Brobbel swept a dipping shot over St Mirren keeper Paul Harrison to give the visitors the lead before half-time.
But in a dramatic four-minute spell, Stephen McGinn rifled in a 25-yarder before TNS' Steven Saunders saw red and Stevie Mallan curled in the free-kick.
John Sutton added a third before Rory Loy grabbed the fourth in injury time.
Two minutes earlier before his goal, Sutton had a penalty saved by Harrison, but the veteran striker made no mistake as he tucked home a Kyle Magennis cut-back from the right flank.
The final, at a venue yet to be confirmed, will take place on the weekend of 25/26 March. United won 3-2 at Queen of the South in Saturday's first semi-final.