INVERNESS Caledonian Thistle have a team that delivers more than Santa.

The remarkable season unfolding for the club will suffer setbacks sooner or later but not here, when they coped with Ross County just as they had recently dealt with Rangers, Celtic, Aberdeen, Hibernian and others. Second in the SPL, into a League Cup final, and now the victors in a tense fourth-round replay against the neighbours.

They are at Kilmarnock in the fifth round and right now the best thing about that, from the host's point of view, is the date. Maybe by February 2 Inverness's rich form will have ebbed. Surely Billy McKay will not still be scoring as prodigiously then as he is now. His two goals – a penalty and then a sumptuous winner –decided this otherwise hard-fought but drab derby.

The double took him to 13 for the season and seven in his last five games. Before kick-off the public address announcer introduced with this: "he scores when he wants . . . Billy McKay", and it almost seems as though he does.

Terry Butcher, the home manager, embraced a precious win after an ordinary display. "Playing like that, it was a great game to win. I'm just delighted to be through, to be honest. It was a very poor game and Ross County put us under a lot of pressure. We didn't get our passing going the way we normally do. The one bit of quality that stood out for me was Billy McKay's second goal. It's a good job we have Billy: it didn't look as if anyone else was going to score for us tonight! He's growing in confidence all the time. He's getting the attention and the rewards now, thank God we've got him tied up for another year."

Inverness have now won two and drawn the other of the three Highland derbies this season. County had by far the best of the second half but the hosts kept them at bay. The rivalry between the fans and players burned intensely enough for some heat to pierce the bitter weather. It was five below zero at kick-off. The pitch looked as though it had been dusted with icing sugar. The football was raw.

The incident which put Inverness ahead in only the eighth minute could have been custom-designed to make Ross Couty manager Derek Adams blow a gasket. First County conceded a cheap free-kick down their opponents' right. Then, when Aaron Doran swung over a delivery, Ross Tokely and Gary Warren scrambled together in the box, yet referee Craig Thomson saw Warren as a victim and Tokely an aggressor. Inverness had a penalty and McKay his first goal, sending Mark Brown one way and the ball the other.

"It was another big decision in the cup tie," said Adams. "There were a number of big decisions and they haven't gone for us. Grant Munro feels that he should have had a penalty in the second half. Overall the best team has gone out, obviously, we had more possession and more opportunities."

Caley Thistle were the better side only for parts of the first half but they, like County during their decent spell during the middle of the first 45, barely threatened other than when scoring once. Doran was lively and had the beating of Marc Fitzpatrick but he didn't get into the game enough to worry County.

County had made it 1-1 with a delicious goal. Colin McMenamin made a minimal overall impression on the match but he could at least claim an involvement in his team's best moment of the night. It was his headed flick-on which gave the ball to the excellent Iain Vigurs, although what came next was purely down to the forward's fine individualism. He had both the vision to see Antonio Reguero off his line and also the technique to apply a wonderful half-volley which sent the ball soaring over the goalkeeper into his net. It continued County's curious habit of scoring fine goals against Caley Thistle, even in defeat.

The winner in 54 minutes was a match for County's goal, another finish applied with real aplomb. Andrew Shinnie drove forward and although substitute Munro blocked him the ball merely broke to an even greater danger, McKay. He was composed and precise in sweeping the ball inside Brown's far post.

County's character was beyond criticism. Their response to falling behind again was to put Caley Thistle under sustained pressure until the very end. Vigurs had a glorious chance with a close header but directed it straight into Reguero. Owain Tudur-Jones hacked the ball off the line in another County attack, and McMenamin should have done better than drive a shot past the post after getting in behind the Caley Thistle defence. Butcher's team was holding on, but they were also defending with organisation and diligence.

County ache to beat them, and will get another chance when they meet again in Dingwall at the start of the year. "Oh, I look forward to January 2," said Adams. "I wish it was tomorrow, because there are a few smirks to wipe off a few peoples' faces."