Celtic had made a dream start with Gary Mackay-Steven opening the scoring after just 25 seconds but Martin Woods levelled matters from the penalty spot in the 15th minute after Efe Ambrose was sent off for bringing down Alex Schalk.

County moved ahead in the 48th minute courtesy of a Paul Quinn header before Schalk made it 3-1 15 minutes later with a shot into the roof of the net from a tight angle.

Leigh Griffiths then saw his 76th minute penalty saved as County, who famously knocked Celtic out of the Scottish Cup at the same stage in 2010 while they were a First Division side, held on to send the holders out and end the Glasgow giants' hopes of a domestic treble.

"I think we started very well. The first 10 minutes was very good. We created three or four chances and we scored a beautiful goal," Celtic manager Ronny Deila said.

"We had everything in our hands and then of course the red card changed everything again. Playing 80 minutes with 10 men made it hard for us."

County will now face Hibernian, who knocked out St Johnstone in Saturday's semi-final, in the final on March 13.

"We are absolutely delighted. We felt we had the toughest task in the two semi-finals and we got off to the worst possible start," County manager Jim McIntyre said.

"It means everything to the club to get to the League Cup final for the first time."

Celtic's start couldn't have been better as Callum McGregor threaded a ball between two Ross County players for Griffiths who rolled the ball across the box for Mackay-Steven to tap in.

Ambrose then had a header cleared off the line from Richard Foster as Celtic came close to adding another.

County didn't take long to settle and soon had a chance of their own as Schalk forced Craig Gordon into a superb save with a rasping strike from the edge of the box.

A moment of madness from Ambrose then allowed County to level the match. 

Jackson Irvine's clever flick released Schalk and the striker was sent tumbling to the ground following contact with Ambrose. 

Referee Craig Thomson didn't hesitate in showing the Celtic defender a straight red card and Woods expertly despatched the resultant penalty as he sent Gordon the wrong way.

Deila brought on new signing Erik Sviatchenko for his debut as he reorganised his side and it was the Hoops who continued to press despite being down to 10 men. 

Stuart Armstrong came close with a curling effort that landed on the roof of the net before County 'keeper Scott Fox parried a Mikel Lustig header before bravely saving at the feet of Nir Bitton and Sviatchenko.

Ross County soon made their extra man advantage count with a goal just over two minutes after the restart. 

Captain Andrew Davies did well to stretch and head a corner to the back post back into the centre of the six-yard box where Quinn bulleted a header past Gordon.

County then exploited the gaps in Celtic's defence to move further ahead in the 63rd minute. 

Irvine threaded a pass to Schalk down the inside left-channel and the Dutch striker unleashed a powerful strike from a tight angle that flew into the roof of the net.

Celtic were presented with a golden chance in the 76th minute when referee Thomson awarded a penalty when substitute Brian Graham handled in the box but Griffiths, normally deadly from the spot, saw his effort kept out by the legs of Fox.