Motherwell 3 Aberdeen 0
Curtis Main struck twice as Motherwell swept Aberdeen aside 3-0 at Hampden to reach their second cup final of the season.
Main and Ryan Bowman scored inside two minutes of each other midway through the first half of the William Hill Scottish Cup semi-final.
And Main struck his eighth goal since joining Motherwell from Portsmouth in January when he raced from the halfway line to net on the counter-attack in the 66th minute.
There was more than a hint of handball in the build-up to the opener but the Betfred Cup runners-up ended up convincing winners as Aberdeen paid for being unable to deal with three high balls.
Aberdeen struggled without the suspended Shay Logan, Graeme Shinnie and Kenny McLean. Dominic Ball came in at right-back while Chidi Nwakali started in midfield alongside Anthony O'Connor.
Motherwell boss Stephen Robinson also had three key players missing as suspended captain Carl McHugh joined long-term absentees Peter Hartley and Craig Tanner on the sidelines. But they had Allan Campbell, Andy Rose and Charles Dunne starting following injury.
Aberdeen made the brighter start but Motherwell's midfield trio of Campbell, Rose and Liam Grimshaw soon got on top through sheer work-rate and desire.
The Dons had snuffed out Motherwell's physical threat in their recent 2-0 win at Fir Park with the same central defensive line-up of Scott McKenna and Kari Arnason, with O'Connor offering extra protection just in front.
But they were unable to deal with Trevor Carson's long free-kick as Motherwell took the lead in the 20th minute.
Arnason could only head the ball behind him and Tait got in front of Ball, who stopped to appeal after the ball bounced off the stand-in skipper's arm. But referee Kevin Clancy or Tait did not and Main tapped home the cut-back.
Aberdeen's defending was even less impressive three minutes later. McKenna sliced a clearance back to the edge of his box and Bowman outmuscled Arnason before finishing at the second attempt after Joe Lewis had spilled his volley.
Bowman cut inside Arnason and forced a save from Lewis moments later before Motherwell set about protecting their lead.
Aberdeen boss Derek McInnes had to speed up his inevitable reshuffle when Nwakali went over on his ankle two minutes before half-time but substitute Gary Mackay-Steven soon set up their first real chance, only for Stevie May to screw well wide from 10 yards.
Aberdeen made little impact going forward in the early stages of the second half, though, and McInnes went for broke in the 61st minute with winger Niall McGinn replacing Ball to give them six attack-minded players on the pitch.
McGinn immediately set up a chance for Adam Rooney but Carson made his first save of the game to parry wide.
Just as Aberdeen seemed to be putting Motherwell under pressure, they were hit with a sucker-punch.
Arnason volleyed Tom Aldred's long ball off Main on the halfway line and the striker had a clear run for goal. The former Middlesbrough man kept his composure to finish high into the net from 20 yards.
McGinn volleyed over but Aberdeen never really threatened a comeback as Motherwell set up a Hampden return against Celtic or Rangers on May 19.