All too often in derby matches Irvine have been guilty of allowing themselves to become caught up in the niggle and forget that there is a rugby match to be won, but on this occasion they managed to concentrate on playing their rugby and let their opponents self-destruct - and reaped the rewards.
Irvine remain seventh in the league, with sixth-placed Helensburgh also winning, but with other results going Irvine's way they are now in the mix in mid-table and a good top-half finish is not beyond them if they can build on this victory.
The visitors were first on the board after 10 minutes, fly-half Colin Sturgeon kicking a penalty after the hosts infringed in defence following a good break by winger Paul Ramsay.
The game remained cagey after this but the home side's chances received a boost when visiting hooker MacKenzie Pearce earned himself a yellow card for persistent infringements midway through the first half. Irvine stepped up the pace and earned their reward shortly afterwards in the form of a penalty under the posts, which Ross Bryan goaled to square the match.
There was no further scoring in the power play, but the momentum was definitely with Irvine now and it was no surprise when they took the lead shortly after the half hour. The home forwards forced a penalty for collapsing a maul which was kicked to the corner, and from the resulting lineout they again mauled towards the Kilmarnock line, creating the space for Craig Maxwell to peel off and score his first competitive try for Irvine in the corner.
As if in tribute to this milestone, as well as the try's importance in the context of Irvine's season, Ross Bryan produced his finest conversion kick of the season, beautifully fading the ball inside the near post to make it 10-3. And he edged the home side further in front with another penalty just before half time when the visiting forwards halted another driving maul illegally, to take the score to 13-3 in the hosts' favour at the interval.
Kilmarnock came flying out of the traps after the restart, and should have scored inside the first two minutes. First winger Chris Milligan raced for the line and his progress was only halted by a high tackle. The visitors then opted for a scrum from the resulting penalty, but the home forwards turned the ball over and the chance was lost.
Bryan and Sturgeon exchanged penalty misses in the ensuing minutes, before the Kilmarnock fly-half received the second yellow card of the afternoon on 56 minutes for serious foul play in his own half. This time Bryan made no mistake to put the home side 16-3 up.
Irvine capitalised on their numerical advantage just after the hour. The visitors looked to have the situation under control when they won a penalty in their own 22, but opted to try to play rugby out of defence when conservatism should perhaps have won out - and Neil McMillan punished them by intercepting an over-elaborate pass and running in his second try in as many games. Bryan again converted for a 23-3 lead.
Irvine pride themselves on being one of the more hospitable clubs to visit in Scotland and duly returned the compliment by conceding an equally soft try shortly afterwards, allowing Milligan to run from his own half to score the try he had threatened earlier. Sturgeon, in his first act after coming back on from his sin-binning, trimmed the deficit to 23-10 with his conversion.
The visitors' discipline continued to be their undoing however, and Bryan added another penalty for Irvine with four minutes to go to put the game out of their reach. There was still time for centre Johnny Bradford to score an unconverted try for Kilmarnock, but it was too little, too late from their perspective and Irvine were able to celebrate victory at last.
Marress remain in the hunt for promotion in their league after a 27-17 bonus-point victory over their Stewartry counterparts, through tries from John Murdoch, Jordan Marshall, Martin McGonigal, Craig Williams and Steven Paton, and a conversion by Stuart Tracey. Their next league game is at home to Cambuslang in a fortnight.
IRVINE -- K Hobson; N McMillan, C Lang, R Filander, C Hobson; R Bryan,
R McVey; D Kirkwood, M Kirk, S Docherty, R O'Neill, A Thomson, A Lang,
C Maxwell, I Speirs.
Replacements: A Nugent, S Nunan, J Doolan, G Gibson.
KILMARNOCK -- G Montgomery; P Ramsay, J Bradford, S Christie,
C Milligan; C Sturgeon, F Porter; D McLeod, M Pearce, B McKay, K Grant,
G Dick, G Andrew, J Brown, G Laurie.
Replacements: T McMichael, R Murray, R Anderson.
REFEREE -- Eddie Rea
MAN OF THE MATCH -- Michael Kirk (Irvine)
MASCOT -- Amanveer Singh Gill