Motherwell 3 - 0 St Johnstone
Motherwell made their first Scottish Cup final for 20 years after a first-half demolition of St Johnstone.
Stephen Criagan nodded the Steelmen in front after just five minutes when Saints goalkeeper Peter Enckelman failed to deal with a corner.
Jamie Murphy doubled their lead soon after with a fine run and low shot.
John Sutton effectively killed off the game before the break with a superb 35 yard volley, although Murray Davidson hit the bar for Saints near the end.
Motherwell will now have the chance to win their third Scottish Cup on 21 May against the winner of Sunday's other semi-final between Aberdeen and Celtic.
No St Johnstone player had scored against SPL opposition since 2 February, but they almost changed that statistic within 90 seconds at the national stadium.
Danny Grainger whipped free-kick into the Motherwell box, which Danny Invincibile flicked on from the penalty spot, and goalkeeper Darren Randolph had to dive acrobatically to tip the ball over the bar.
But Saints' good start was undone minutes later, when Randolph's opposite number Enckelman was badly at fault to allow Motherwell to take the lead.
The Finn completely missed an attempt to punch the ball away at a corner, and Steelmen captain Craigan gratefully nodded in from close range.
And soon after Well doubled their lead, despite good fortune in the build-up when they retained possession in midfield after a slack pass bounced off referee Iain Brines.
Jamie Murphy received the ball, ran with it across the box while Saints defence backed off, and then fired a low shot across Enckelman inside the far post.
Murray Davidson almost replied immediately from a bizarre ricochet off a Craigan clearance, and the Saints midfielder watched another shot from 25 yards sail just over.
But those were interlusdes in what was fast becoming a very one-sided affair.
Motherwell should have made it 3-0 after half-an-hour, when Keith Lasley jinked past Dave Mackay before he shot wide from a good position in the box.
Then Murphy almost scored after another solo run from deep in the midfield, but this time his shot went the wrong side of the post by an inch.
Well took a third goal before the break in spectacular fashion.
Randolph pumped the ball long towards his forwards, Francis Jeffers nodded in back towards the advancing Sutton.
And the Englishman continued his record of scoring in every round of this year's cup, smashing a fierce dipping volley over Enckelman from fully 35 yards - although again the Saints number one's positioning was suspect.
St Johnstone began the second period with more urgency and Davidson was frustrated by Randolph as the Well goalkeeper tipped over his fine strike from 25 yards.
Grainger also had a free-kick on target, although it did not trouble Randolph, who held it easily.
But, Motherwell had done the damage in the first 45 minutes and Saints' afternoon was summed up when Davidson watched a late header crash back off the bar with Randolph beaten.
