United's dream of taking the Scottish Cup back to Tannadice for a third time was dashed at the final attempt as they succumbed to defeat by St Johnstone at Celtic Park.
Jackie McNamara's talented young squad have nothing left to show for a season that at times promised so much, after a spirited Perth side scored late in both halves through Steven Anderson and Steven MacLean to secure their first ever piece of silverware.
The outcome could have been different, though, with United twice hitting the woodwork and missing a series of chances.
It was a day to forget for the 30,000 Arabs who cheered their side on - the biggest ever sea of tangerine created at a United match.
It was a clash of footballing styles, with McNamara opting for his usual passing approach against the direct, pressing and energetic St Johnstone side.
Both sides started at a high tempo and United were the first to threaten, with Ryan Dow pinging in a cross from the right that Alan Mannus fumbled under pressure as Nadir Ciftci lurked threateningly.
St Johnstone started to enjoy a lot of possession in United's half and were the better side for the first 25 minutes of the game. In that period, they so nearly broke the deadlock when a spectacular effort from midfielder James Dunne had to be acrobatically tipped over the bar from Radoslaw Cierzniak. The resultant corner dropped invitingly at the feet of Dave Mackay but Cierzniak managed to get down well to gather at his feet.
Although United were looking menacing at times, it was the Perth side that was continuing to create the better chances and they again nearly took the lead when a Steven Anderson shot took a wicked deflection off Gavin Gunning right in front of goal and nearly spun into the net, only for an alert Cierzniak to change his direction and collect.
An almighty scramble in the St Johnstone box then nearly gave United the lead, as Ryan Dow neatly played in Stuart Armstrong, with his ball across the goal being blasted off Frazer Wright's arm by his fellow centre half.
United were starting to gain some momentum, and enjoyed a strong spell in the final quarter of an hour of the half. They won a corner when Dave Mackay tackled Robertson after a spirited run up the left by the young player of the year. Dow's corner picked out Gunning at the back post but he headed wide.
United then so nearly went ahead with an outstanding effort after a great move. A fine passing move quickly swept the ball from one side of the park to the other, with John Rankin unleashing a rampaging Robertson, who put in a brilliant cross which was met by a wonderful flick by Dow that beat Mannus but spun off the inside of the post before being hacked away for a corner.
The Tangerines had the bit between their teeth and were finishing the half strongly, with Ryan Dow and Andy Robertson in particular causing Saints constant problems down the left. United were denied a penalty when Dow tried to sweep a ball into the box only for it to appear to smack off Anderson's arm and go out for a corner.
However, despite a period of being well on top, United found themselves going in at half-time 1-0 down when St Johnstone took the lead just inside injury time. Andy Robertson had to be alert to head a cross from the left behind for a corner. Cierzniak missed the cross from the corner and Anderson leapt above the keeper and Sean Dillon to head home.
The second half got underway with some blistering action in an utterly frantic spell. Saints somehow stayed ahead when a Nadir Ciftci free kick from the edge of the box curled and dipped then hit the underside of the bar and nearly went in off Mannus on the rebound.
St Johnstone then thought they had gone 2-0 up when Steven MacLean had the ball in the net - only for the linesman to spot that he had punched the ball over the line despite referee Craig Thomson appearing like he was going to give the goal.
Paton was then booked for a feisty challenge on the halfway line and Ciftci curled a free-kick over the bar in a blistering first 10 minutes of the second half.
The action continued thick and fast and first David Wotherspoon went on a long winding run past several United challenges before his effort was saved by Cierzniak.
Then Robertson did exactly the same at the other end as
Robertson went on a mazy dribble before curling in an outstanding effort from outside the box which Mannus tipped behind.
Ryan Gauld was given just under half an hour of action, as he came on for Mackay-Steven, who appeared to be struggling after taking a knock.
United kept putting the St Johnstone defence under pressure as the ball ping-ponged around Alan Mannus' box. When Rankin headed into the box Dow nearly got on the end of it only for Mannus to parry away as Armstrong desperately lunged for it.
With just over 10 minutes to go, Brian Graham - on for Paul Paton - had a chance when a wayward Gunning effort fell to him, only for the striker's effort to curl just wide.
Nadir Ciftci then showed some great footwork to evade a few challenges then send a powerful fizzing effort just wide of the post from outside the box.
With five minutes to go, St Johnstone went into a two-goal lead in controversial circumstances. A through ball bobbled into the box to Stevie May and, although Cierzniak managed to spread himself to save the first effort, May followed through to trundle the ball over the line, despite the keeper's claims that he was fouled.
United tried to rescue what looked like a lost cause, and a long-range effort from Dow was easily held by Mannus. In injury time, a close-range effort from Armstrong was deflected behind then a Graham header right in front of goal went just past the post but it just wasn't to be the Tangerines' day.
ST JOHNSTONE:
Mannus; Mackay, Wright, Anderson, Easton; O'Halloran (Croft, 72), Millar, Wotherspoon (McDonald, 85), Dunne; MacLean, May
Subs: Banks, Cregg, Hasselbaink, Miller, Iwelumo
UNITED: Cierzniak; Watson, Robertson, Gunning, Dillon; Rankin, Paton (Graham, 76); Dow, Armstrong, Mackay Steven (Gauld, 63); Ciftci
Subs: McCallum, Wilson, Souttar, Gomis, El Alagui