Match ends, Kilmarnock 3(4), St. Mirren 3(5).
Referee Don Robertson "changed the whole game" as St Mirren triumphed in a Scottish Cup quarter-final thriller, says Kilmarnock manager Tommy Wright.
The official awarded a controversial penalty to each side at Rugby Park, with the visitors coming out on top 5-4 on spot-kicks after a 3-3 draw.
And Wright was blunt over Robertson's 119th-minute penalty award for Jamie McGrath to send the tie to a shootout.
"It's extremely disappointing," he said.
"Let's be honest, Don Robertson put it into penalties with a poor decision. When he is man enough he will own up to it.
"I will go and see him after the game. Over the years I have been in to see Don more than any other ref."
Robertson judged Kilmarnock goalkeeper Colin Doyle to have fouled Jake Doyle-Hayes inside the box with the hosts seconds from a 3-2 win in extra time.
Television replays appear to show Doyle taking the ball before bringing down the St Mirren man.
"We could have dealt with the situation better, [Ross] Millen could possibly just put his foot through it, but it is not a penalty all day long," added Wright.
"The goalkeeper clearly gets the ball, the fact that it spills out is irrelevant. No penalty. But Don wanted to have the final say and he got it."
Jim Goodwin's side will take on League Cup winners St Johnstone on 8 or 9 May, with Dundee United facing Hibernian in the other semi-final, and his team will be dreaming of what could be after a rollercoaster night in Ayrshire.
George Oakley and Greg Kiltie were off target for the hosts, who were without in-form Kyle Lafferty, before they fell behind.
Ilkay Durmus was released on the right from a free-kick and his cross went through Doyle's grasp into the net.
The ever reliable Chris Burke produced a superb corner delivery for Kilmarnock's leveller, Ibsen Rossi powering the ball home.
Oakley was the architect of Kilmarnock's second, bustling down the right and squaring for Kiltie to convert.
Kilmarnock could have put themselves out of sight with Kiltie testing Jak Alnwick then crossing for Oakley to turn over.
McGrath had curled an effort wide and it was his free-kick that led to St Mirren's equaliser, the inswinging delivery from the left expertly helped on by Joe Shaughnessy.
And substitute Collin Quaner could have won it for Jim Goodwin's side in regulation time, his shot well saved by Doyle.
Extra time ensued and Kilmarnock had used all their substitutes by the time Oakley's replacement Nicke Kabamba picked up a knock after shooting wide, leaving them with 10 men.
And there was more drama when Brandon Haunstrup chased Alan Power's pass and referee Robertson judged Kyle McAllister's challenge to be illegal. Ross Millen fired down the middle from 12 yards.
But there was another twist in the tale as Doyle-Hayes was felled by Doyle to allow McGrath to stroke in the game's sixth goal.
Doyle partially redeemed himself by turning Shaughnessy's header over in the 120th minute.
McKenzie was the only player not to score in the shootout, with McAllister having the last laugh in the third quarter-final settled by penalties.
Man of the match - Greg Kiltie
Kiltie was the best player over 90 minutes, scoring one and unfortunate not to add to his tally.
What did we learn?
With Celtic and Rangers already out, both sides knew this season presented a real opportunity to win the tournament.
And for 1987 winners St Mirren, a semi-final place offers another chance at glory after losing to Livingston in the last four of the League Cup and missing out on a Premiership top-six place.
Lafferty's absence did not hinder Kilmarnock quite as much as expected, and ultimately it was defensive lapses that cost them.
Top-flight survival remains their priority, with Wright's team two points above the relegation zone with three games left.
What did they say?
St Mirren manager Jim Goodwin: "We were all going through the ringer tonight. Some of the goals we conceded were shocking.
"Great credit to the players for their character and willingness to go right to the end. We're there, that's all that matters. St Johnstone might be favourites for the cup. It'll be a good game and we look forward to it."
Kilmarnock visit Motherwell in the Premiership on Saturday (15:00 BST) while St Mirren are at home to bottom side Hamilton Academical (15:00).
- 29BurkeSubstituted forDickerat 90'minutesBooked at 108mins
- 21MulumbuSubstituted forTshibolaat 76'minutesBooked at 90mins
- 10KiltieSubstituted forMcKenzieat 90'minutes
- 9OakleyBooked at 66minsSubstituted forKabambaat 81'minutesSubstituted forat 96'minutes
- 1AlnwickBooked at 101mins
- 22FraserSubstituted forMacPhersonat 105'minutes
- 5McCarthyBooked at 82mins
- 11DurmusSubstituted forMcAllisterat 72'minutesBooked at 101mins
- 20DennisSubstituted forQuanerat 61'minutes
- 23ErwinSubstituted forErhahonat 61'minutes
- Don Robertson
- Shots on Target
Penalty Shootout ends, Kilmarnock 3(4), St. Mirren 3(5).
Goal! Kilmarnock 3(4), St. Mirren 3(5). Kyle McAllister (St. Mirren) converts the penalty with a left footed shot to the top right corner.
Goal! Kilmarnock 3(4), St. Mirren 3(4). Aaron Tshibola (Kilmarnock) converts the penalty with a right footed shot to the centre of the goal.
Goal! Kilmarnock 3(3), St. Mirren 3(4). Joe Shaughnessy (St. Mirren) converts the penalty with a right footed shot to the bottom right corner.
Goal! Kilmarnock 3(3), St. Mirren 3(3). Ross Millen (Kilmarnock) converts the penalty with a right footed shot to the top right corner.
Goal! Kilmarnock 3(2), St. Mirren 3(3). Collin Quaner (St. Mirren) converts the penalty with a right footed shot to the bottom right corner.
Goal! Kilmarnock 3(2), St. Mirren 3(2). Mitchell Pinnock (Kilmarnock) converts the penalty with a left footed shot to the top right corner.
Goal! Kilmarnock 3(1), St. Mirren 3(2). Cameron MacPherson (St. Mirren) converts the penalty with a right footed shot to the bottom right corner.
Penalty saved! Rory McKenzie (Kilmarnock) fails to capitalise on this great opportunity, right footed shot saved in the centre of the goal.
Goal! Kilmarnock 3(1), St. Mirren 3(1). Jamie McGrath (St. Mirren) converts the penalty with a right footed shot to the bottom right corner.
Goal! Kilmarnock 3(1), St. Mirren 3. Gary Dicker (Kilmarnock) converts the penalty with a right footed shot to the bottom right corner.
Penalty Shootout begins Kilmarnock 3, St. Mirren 3.
Second Half Extra Time ends, Kilmarnock 3, St. Mirren 3.
Corner, St. Mirren. Conceded by Colin Doyle.
Attempt saved. Joe Shaughnessy (St. Mirren) header from the centre of the box is saved in the top centre of the goal.
Goal! Kilmarnock 3, St. Mirren 3. Jamie McGrath (St. Mirren) converts the penalty with a right footed shot to the centre of the goal.
Penalty St. Mirren. Jake Doyle-Hayes draws a foul in the penalty area.
Penalty conceded by Colin Doyle (Kilmarnock) after a foul in the penalty area.
Foul by Jay Henderson (St. Mirren).