Not only does absence make hearts grow fonder, it can apparently intensify rivalry. Even at their respective football peaks, Ayr United and Kilmarnock weren't accustomed to frequent competitive meetings. As Kilmarnock became champions of Scotland, in 1965, Ayr were forced to re-apply for membership of the league after finishing last but one in the Second Division. Ayr's supporters, that said, take great delight in highlighting a 1-0 victory over Kilmarnock in the Ayrshire Cup final just days after that title had been secured.

Almost a decade later, it was Kilmarnock who toiled in a lower tier as Ayr enjoyed their most heady days in the top flight. It is little wonder, then, that Saturday's League Cup semi-final between these old foes is billed as the most significant Ayrshire derby ever.

The fierce nature of this fixture may be lost on those beyond the towns and villages of Ayrshire whose inhabitants will descend on Hampden Park. Or anybody who has not previously attended an Ayrshire derby. The ferocity, not least of language emanating from stands and terraces, is quite something to behold.

These towns lie 13 miles apart. Geographically, it is roughly suggested that support is split around Symington; with those north of that village following Kilmarnock and fans further south opting for Ayr.

"I'm trying to be unbiased about it but I think the fixture tends to be a bigger attraction and means more to Ayr than to Kilmarnock," suggests Ronnie Hamilton, the youngest player to turn out for Kilmarnock in a Scottish league match and later the club chairman. "Kilmarnock are the bigger club, with the better pedigree. It always seems easier for Ayr to raise their game."

Such sentiment is hotly disputed by Duncan Carmichael, Ayr's club historian. "Kilmarnock had a huge win over Rangers in 1994 and their supporters were singing anti-Ayr songs in celebration," he says. "Ayr were struggling at the time. No matter the league gap between us, Kilmarnock's supporters will be singing anti-Ayr songs. They are as bothered, all right. Rangers and Celtic supporters, even the hot-headed ones, have an element of mutual respect after a derby. With Ayr and Kilmarnock, there is an awful lot less give and take."

Kilmarnock lie seventh in the SPL with their part-time opponents sitting second-bottom of the First Division. That roughly paints a picture of history – Kilmarnock as the more prominent and successful club – but Kenny Shiels's men must be wary of complacency, their erratic form aside.

Ayr have won the past four League Cup meetings between the teams and have bundled three SPL sides – Inverness, Hearts and St Mirren – out of this season's competition. In consecutive seasons, 1998 and 1999, Ayr also eliminated Kilmarnock from the Scottish Cup.

"They had won the cup in 1997 so those two wins meant we felt good about ourselves again," Carmichael says. "I would argue this is probably the biggest game in Ayr's history, even although it is far from the best Ayr team. If we win on Saturday, I'll hardly even care about the final. My unfulfilled ambition is to see an open top bus parade a cup through Ayr. This year, there is a probably a better case for having that parade after the semi-final than the final."

Hampden may be only around half-full for this tie, but such an attendance must be put in context. At least 15,000 Kilmarnock supporters are expected in Glasgow. Such numbers weren't even commonplace at Rugby Park almost 50 years ago, when the championship was claimed and Kilmarnock were a regular force in Europe.

Ayr's anticipated following of 8,000 compares favourably with their last two home crowds; 1,310 and 1,407. An inability to move from or redevelop their decrepit Somerset Park home has been a major hindrance to Ayr's plans for progress over the past two decades.

Those who advocate the present, tight set-up of the SPL should take an added interest in the semi-final. Fixtures such as an Ayrshire derby, clearly attractive and lucrative, have been lost amid an unwillingness to move towards league expansion.

"There are smaller numbers of fans than the Glasgow derby, but the rivalry is every bit as intense," says George Burley, the ex-Scotland manager and a native Ayrshireman. "You have to remember how football-orientated Ayrshire is. A lot of top international players have come from there."

For 90 minutes on Glasgow's south side, that wider picture will be totally irrelevant.