A breakaway goal from Bojan Miovski fired 10-man Aberdeeen into the Viaplay Cup final as Hibernian failed to take their chances at Hampden.
A cool 78th-minute finish from the striker was the Dons' first meaningful attempt and came soon after a foolish second booking for Jack MacKenzie.
Miovski squandered a similar chance and picked up a caution for diving in a crazy few moments after scoring.
Hibs, who had a Martin Boyle effort ruled out after a lengthy VAR check, were the brighter side for most of a contest that was sorely lacking in quality but did not threaten enough.
Aberdeen, who last celebrated silverware with this trophy in 2014, will meet Rangers or Hearts in the final on 17 December.
Neither side seemed in much of a hurry in a drab first half, with a lot of ponderous possession, aimless passing and set-pieces taking an age each time.
Hibs were slightly more menacing, with Elie Youan blazing over the top and a Joe Newell effort deflected wide.
Earlier, a sliding Connor Barron did well to knock the ball over his own goal to prevent Boyle meeting Youan's curling cross.
Aberdeen were going long to striker Miovski too often without any success, while captain Graeme Shinnie was guilty of a poor swipe in front of the target.
The second half began with Nicky Devlin clearing a fizzing Lewis Miller delivery from the Aberdeen six-yard box before Boyle thought he had made the breakthrough with a sublime first touch and finish.
After an embarrassing delay filled with jeers and whistles, the VAR room eventually ruled the Hibs forward offside.
It was the spark the game needed as both sets of fans found their voices.
Kelle Roos saved well from Jair Tavares, there were cries for a penalty as the Aberdeen keeper flapped at the feet of Dylan Vente, and Devlin got an important leg in the way of a Boyle rocket.
Aberdeen were looking livelier, too, but were suddenly down to 10 after a moment of madness from MacKenzie. Already on a booking, the wing-back took exception to a nudge from Miller and shoved his opponent over with both hands.
And then, against the odds, the depleted Dons snatched victory.
The Hibs half was empty as Miovski broke clear and no one got near him as he ran on to stroke the ball beyond a hesitant David Marshall.
Miovski then sclaffed an easier opportunity wide and picked up a caution for simulation as a stunned Hibs let him through twice again.
The Edinburgh team piled men forward during seven minutes of added time but could not fashion a serious chance to find a leveller.