Sunderland delivered another crushing blow to David Moyes' tenure at Manchester United by reaching their first domestic cup final since 1992 in dumping the Premier League champions out of the League Cup on penalties.
Trailing 2-1 from the first leg, Jonny Evans' first half header looked to be sending United to Wembley as the game entered the dying embers of extra time but David de Gea's fumble from Phil Bardsley's shot in the 119th minute put the Black Cats on the brink.
Javier Hernandez equalised in stoppage time to take the tie to a penalty shoot-out where Vito Mannone saved twice amid four missed United spot-kicks as Marcos Alonso and Ki Sung-Yueng both scored to take Gus Poyet's relegation threatened Sunderland to Wembley.
Manchester City are their opponents at the club's first showpiece final for 24 years, while a European place it all but assured for next season. For United, the gloom continues despite the imminent signing of Juan Mata from Chelsea.
For so long it appeared as though Moyes would earn temporary respite after going 14 points behind leaders Arsenal following the weekend defeat to Chelsea, after Evans' first half header had the champions ahead.
Sunderland, as has been the way through their rejuvenation under Poyet, never gave in and after surviving missed chances from Hernandez and Adnan Januzaj, leveled with their first shot on target as Bardsley, six years to the day since he left Old Trafford, benefitted from a cataclysmic error from De Gea in the United goal.
However, the celebrations of the 8,000 traveling Weirsiders was premature as United took the tie to penalties with a goal in the first minute of stoppage time as Januzaj exchanged passes with Chris Smalling before crossing for Hernandez to bury from six yards.
But United were unable to take their second chance with both hands and despite Craig Gardner and Steven Fletcher missing Sunderland's first two penalties, Danny Welbeck's miss gave the hosts a narrow advantage following Darren Fletcher's success.
January signing Alonso and Ki, on loan from last year's League Cup winners Swansea City both converted either side of Vito Mannone saving from Adnan Januzaj and though Adam Johnson was unable to take advantage of Phil Jones' skied effort, the Italian stopper denied Rafael to secure Sunderland's place at Wembey.