Nadir Ciftci’s late winner ended Aberdeen’s hopes of retaining the League Cup as Dundee United came from behind to win 2-1.
New signing Donervorn Daniels gave the Dons the lead early in the second half but Callum Morris restored parity on the hour mark before Nadir Ciftci nodded home the winner six minutes from time.
United will now face Celtic or Rangers in the final at Hampden on March 15.
Daniels, who joined the Dons on loan from West Brom on Tuesday, was pitched straight into the starting line-up, partnering Mark Reynolds in the centre of the Dons defence.
United made four alterations from the team that defeated Motherwell 3-1 last weekend with Blair Spittal, Aidan Connolly, Henri Anier and Ryan Dow making way for Paul Paton, Nadir Ciftci, Gary Mackay-Steven and new signing Ryan McGowan, formerly of Shandong Luneng Taishan, who had not played since the Chinese season finished in November
United started brightly and should have opened the scoring within four minutes when Mackay-Steven caught the Dons defence sleeping to race on to a Ciftci free kick but the winger was unable to slot home from an acute angle after rounding Scott Brown.
There was an enjoyable flow to proceedings in the opening stages with both teams attacking at will, although it was United who looked the more likely with Stuart Armstrong trying his luck with a delightful left-footed effort from 20 yards that was deflected on to the crossbar.
Aberdeen were growing into the game as the half wore on but were finding United’s defence more resolute than normal with Peter Pawlett and David Goodwillie both denied by some excellent challenges.
The Dons made the perfect start to the second half when a long throw-in from Andrew Considine was met by new signing Daniels whose looping header evaded everyone and nestled kindly in the back of the net.
Mackay-Steven had an effort ruled out for offside before Daniels was inches away from adding a second only four minutes after his goal but his effort was hooked off the line by Jaroslaw Fojut.
And United found a way back into the match on the hour mark when Callum Morris headed home at the back post from an in-swinging Mackay-Steven cross.
The Dons thought they were back in front three minutes later when Rooney headed home from a McGinn corner but the effort was ruled out by referee Steven McLean for an infringement as a gripping game raced from end to end.
There was no let-up in play as the Dons pushed for the next goal but Czierniak pulled off an instinctive stop to deny Ryan Jack from Niall McGinn’s inviting centre.
United were next to threaten when substitute Ryan Dow slid the ball beyond Brown but Mark Reynolds managed to clear the ball off the line.
But the Tangerines were celebrating the winner in the 86th minute when Ciftci capitalised on some poor Dons defending to nod home a Paul Paton cross.