Kilmarnock booked their ticket to Hampden and will visit the National stadium for the first time in almost 11 years.
The famous League Cup win against Celtic in March 2012 was the last time the Killie faithful could head to the home of Scottish football.
Kyle Lafferty and Dan Armstrong strikes ensured that there would be dancing in the streets of Kilmarnock tonight with a fine Premier Sports Cup victory against Dundee United, the tie will be played on January 14 or 15.
Boss Derek McInnes said: "It was a very big result, there are defining moments in seasons.
"It was 50/50, but we have a strong home record.
"We wanted to play balls into the box but I didn't expect 'big' Danny to score.
"Kilmarnock have been a Premier League team and you'd expect more return from the cups.
"Cup football can galvanise a club. It gives you financial rewards and can help the league form."
Killie fired themselves in the lead thanks to Lafferty’s penalty in the seventh minute after Liam Smith was deemed to have handled the ball.
But the lead barely lasted a minute when Middleton fired an effort into the far left corner.
Lewis Mayo went incredibly close to bagging his first Killie goal but he turned his effort on to the post.
There was little to shout about for either side for a long period until Tony Watt almost fired home from close range, but Zach Hemming got down well to keep the effort out.
It was the home fans on their feet after 71 minutes when Dan Armstrong met a cross with a free header and made no mistake in firing home.
United substitute Steven Fletcher attempted to lob the ball over Hemming in the 87th minute but thankfully for the hosts it hit the top of the net.
Scorer of the winning goal Dan Armstrong told Premier Sports TV: "It's massive. Just to get that win in front of that support was brilliant.
"To send us to Hampden was special and we really enjoyed it.
"The goal was definitely up there in my career.
"We wanted to get the ball in the box tonight.
"Jordan and I had been trying it all night and I was delighted to get in there and get the winner."
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