Fuming David Hopkin slammed whistler Nick Walsh for derailing Ayr's bid to make the last eight of the Premier Sports Cup.
The Honest Men were 1-0 up and had blown a host of good chances to bury Dundee United before Walsh handed the Premiership outfit a late route back into the tie.
The ref's decision to send Jack Baird packing for a pull on Ryan Edwards with 10 minutes to go incensed Hopkin - who was forced to watch Nicky Clark slot home the resultant penalty.
And although Ayr held on for spot kicks, they ultimately went out with hero keeper Benji Siegrist proving a man mountain for the Tangerines.
Hopkin said: "Anybody at the game today could see there was only one team going to win it.
"The decision to give the penalty was horrific.
"The ball was out of the pitch and nobody had even claimed for it.
"Then the referee decides to get involved in the game.
"I asked him about the decision but you don't get any answers.
"And sending Jack [Baird] off turns a fantastic cup tie into a training session.
"But it should never have gone that far - Benji Siegrist has pulled off two world class saves to keep Dundee United in it.
"And I don't think Aidan McAdams has had one save to make for us.
"Dundee United didn't look like scoring, they brought on Mark McNulty and were throwing balls into the box.
"But my centre backs were great and we had a young, exciting side out there today with a couple of Academy players and they were fantastic to a man."
Ayr had taken a well deserved lead just after the break when the impressive Tomi Adeloye found a way past Siegrist.
But they should have put the tie out of sight after that and spurned a host of chances to stretch their lead.
James Maxwell flashed a golden opportunity wide before Siegrist brilliantly denied Paddy Reading and tipped a Mark McKenzie effort on to the bar.
The game was being played in front of a crackling Somerset Park atmosphere and just as Ayr looked like getting over the line, disaster struck with the penalty decision 10 minutes from time.
A ball swung into the box looked to have sailed harmlessly over Edwards' head and out of play before Walsh pointed to the spot for a pull on his shirt.
And the whistler compounded United's anger by dismissing Baird for a second booking.
Clark made no mistake from the spot to send the game to extra time, where the Arabs went close through Clark again and a Liam Smith shot which rattled the post.
They sealed a 4-3 win on penalties with Ayr's Reading and Jonathan Afolabi seeing their efforts saved by Siegrist.
Arabs boss Tom Courts said: "It was a real carnival atmosphere in here today and was always going to be different to what we faced last week against Rangers.
"Real credit to Ayr for the way they played and made it difficult for us.
"But once we got to the penalty shootout it was probably the most comfortable I've been during my managerial career.
"Benji enjoyed the centre stage and was our matchwinner in the end.
"When you look at our previous visits to here in the Championship, I think a draw was our best result, so we always knew it was going to be a tough game."
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