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St Mirren fans flood the pitch as safety is secured

St Mirren preserved their top-flight status - and consigned Dundee United to a fourth season in the second tier - after a nerve-stricken penalty shootout Scottish Premiership play-off final victory in Paisley.

Vaclav Hladky saved United's first two spot-kicks from Peter Pawlett and Pavol Safranko, Osman Sow struck a post with the third, and the Slovakian goalkeeper saved Callum Booth's fourth to ensure St Mirren will spend consecutive seasons in the top flight.

With Thursday's first leg finishing goalless, Championship side United had seized control of the tie thanks to Nicky Clark's 22nd-minute penalty, but the hosts were level with four minutes through Danny Mullen's composed finish and looked the better side throughout the subsequent 94 minutes without finding a winner.

Oran Kearney's side played out the final five minutes of extra time with 10 men after the dismissal of Duckens Nazon, but needed only Paul McGinn and Mihai Popescu to score from the spot to clinch a 2-0 shootout win.

Winds of change not blowing in Paisley

Thursday's goalless first leg was suffocated by tension and this contest was similarly strangled. That said, the unpleasant conditions were just as influential a factor as the nerves. A blustering, swirling wind made judging the flight of the ball devilishly difficult, but it was initially St Mirren who adapted better in front of a first sell-out 8,000 crowd at the Simple Digital Arena.

Benjamin Siegrist, who made two critical interventions at Tannadice, plunged low to his right to push away a Stephen McGinn strike and watched in bemusement as McAllister's sliced effort caught in the wind and carried out for a throw-in.

United were struggling to make the ball stick in the final third, with an approach that was more blood and sweat than pass and move. However, with Safranko preferred to Sow at centre-forward, the St Mirren back three were posed more problems than on Thursday, and it was from the Slovak that the opener stemmed. His adept turn and shot was pushed away by Hladky but Booth's attempt on the rebound struck Jack Baird's arm. Penalty awarded. Clark, composed as you like, rolled the spot-kick into the net.

That moment was to be as good as it got for United, though. Within four minutes, St Mirren were level as a befuddled Mark Connolly slashed at a clearance, sending the ball spinning into the path of Mullen. With a calmness equal to that shown by Clark, the striker strode forward and rolled under Siegrist to spark Paisley pandemonium.

Mullen, benched for the first leg after becoming a father last week, was a persistent pest. Within a couple of minutes of the goal, he fed McAllister to plant a finish past Siegrist, only for an offside flag to smother the celebrations.

Clark and Stephen McGinn fizzed past the frame of the goal at either end before a frantic opening half drew to a conclusion, and that theme of spurned opportunities was to continue after the break, with McAllister tugging wide from a Mullen cross and shanking off target after being picked out at the back post.

St Mirren were, at least, creating chances. Apart from a Paul Watson header that was pushed wide, United were inert. Robbie Neilson introduced Pawlett and Sow in an attempt to fashion a spark but it was the Premiership side who continued to have the better of it.

Siegrist had to be alert to thwart Cody Cooke, then the Swiss made a stunning reaction save to push Paul McGinn's header over the bar after the wing-back steamed at the back post to meet a Lee Hodson cross.

United were hanging on, their 1500-strong support watching helplessly from the other end of the ground, but they survived to take the game into an additional 30 minutes.

Once more, though, they had to rely on Siegrist to keep them level in extra time, the goalkeeper shovelling away after defender Connolly jabbed a Nazon's cross towards his own goal. And those two were to the fore again shortly afterwards, with the striker claiming he was blocked as he bore down on goal only for referee John Beaton to dismiss his disgruntlement.

Sow tugged a shot wide for United and Cooke twice went close for St Mirren. Siegrist - United's best performer by a distance - pushed a Jack Baird drive past and Nazon squirted one either side of the goal posts.

Tension was rife and it was ratcheted up that little bit further when substitute Nazon was dismissed for catching Connolly with a flailing elbow in the latest act of their fleetingly epic duel. United, though, could not make the best of their numerical advantage in the final five minutes, meaning a shootout was needed to determined which of these sides would be in the Premiership next term.

United went to pieces from the spot, though, failing to score any of their four penalties rendering Mateo Muzek's miss meaningless and condemning the Tannadice side to a fifth year since 1960 in the second tier.

Callum Booth's failed penalty sealed victory for St Mirren

'It's been a long, difficult season'

Former Dundee manager and BBC Scotland pundit Jim Duffy

For the club and the town of Paisley, it is vital that they've got a team in the Premiership. It's been a long, difficult season. But they've managed to overcome all the difficulties.