This may have been the most significant Ayrshire derby in history but it was also one of the ugliest. In proving the old adage about semi-finals rarely being entertaining contests, Ayr United and Kilmarnock served up a 120-minute encounter that in spells could have made the eyes bleed. Kilmarnock will regard that as irrelevant; they earned an opportunity to break a League Cup final hoodoo thanks to Dean Shiels's extra-time winner.

More pertinently, that intervention earned Kilmarnock bragging rights over their local foes. The only visible battling thereafter was of the verbal kind, between the managers.

In Kilmarnock's defence, they offered elements of enterprise. Ayr's policy from the early minutes seemed perfectly clear; to make it to a penalty shoot-out and take their chances. Kenny Shiels, the victorious manager, was unimpressed. "I'm relieved because football was the winner," he said.

"Football is about entertainment, people pay money to be entertained. The easiest thing in the game is to defend, anybody can do that. It was a negative approach. I have never played like that, ever. I'm not hammering Ayr United, I'm just saying it would have been a better game if they had come out."

There is a debate to be had about the motivation behind Ayr's tactic, whether or not they were forced upon the manager, Brian Reid, due to a lack of resource or the First Division team were deliberately defensive. Scots can hardly be prissy about the approach, given the national team has profited and been praised for similar against superior opposition.

It made for an unattractive spectacle. Even more frustrating for any neutrals was the fact Ayr actually caused worry in the Kilmarnock defence after the goal.

"Kenny should keep his opinions to himself," said Reid. "He should comment on his own team, not other teams. Nobody would be saying that if we were through to the final."

A crowd in excess of 25,000 – the majority from Kilmarnock – turned out for a game that epitomised the spirit of what has been renamed the Scottish Communities League Cup. Families descended en masse on Hampden from Ayrshire, youngsters therefore indoctrinated into the fierce dislike these two sides have for each other, if they were not already aware. Only the dismal acoustics of Scotland's national stadium blunted the atmosphere.

The first 20 minutes would be described only through necessity. Kilmarnock wasted a series of first-half corners, the Ayr defender John Robertson subsequently heading a Garry Hay cross clear from just in front of his own goal. Shiels and Ben Gordon passed up Kilmarnock chances before the break but it was after the interval that the Premier League team stepped up their pressure. In spells, it resembled an attack versus defence training game.

James Dayton, Paul Heffernan, Hay and Gordon spurned Kilmarnock opportunities. The Ayr goalkeeper, Kevin Cuthbert, is also due credit for a superb save from Gary Harkins's close-range shot. Andy Geggan made sure Cameron Bell in the Kilmarnock goal was still awake with a long-range effort, seven minutes from the end of normal time.

Fittingly, the breakthrough arrived in untidy circumstances. Shiels and Heffernan saw shots blocked by Cuthbert before the manager's son stole back in to slam home. A Mark Roberts cross offered Ayr their best hope of a recovery, Kilmarnock's David Silva heading inches wide of his own goal amid panic.

Kilmarnock have lost all their previous five appearances in a League Cup final. On 18 March, either Celtic or Falkirk stand between Kilmarnock's class of 2012 and making history.