Airdrie will need to turnaround a 1-0 deficit after a Championship play-off semi-final first leg defeat away at Montrose.
Craig Johnston opened the scoring for the hosts after miscommunication in Airdrie's defence between left-back Brody Paterson and goalkeeper Max Currie.
Sean Dillon had an effort hooked off the Airdrie line as Stewart Petrie's side stormed into control of the tie.
Dylan Easton soon hit the post as Ian Murray's visiting side look to strike back and find the form that saw them end their League One campaign 20 games unbeaten.
They'll now need to show powers of recovery during Saturday's second leg on home soil at the Penny Cars Stadium after a rare loss.
Murray made nine changes to his rotated Diamonds that drew 1-1 with Peterhead on Saturday, with only Dunfermline loanee Kyle MacDonald and forward Gabby McGill remaining.
Both sides suffered pain at the play-off stage last year, with Airdrie looking to go one better than their final defeat to Morton, while Montrose were looking to make amends for their last four loss against the same opposition.
The New Broomhill club arrived at Links Park with a club-record 20-game unbeaten league run behind them but coming up against the last team to beat them in league action, way back in December, they were wary.
Michael Gardyne's free-kick into their box on four minutes showed them why. His cross was put into a dangerous area asking for a tap-in but nobody could turn it home.
Montrose had started brighter than their visitors but they didn't have to work hard for their opener on nine minutes. It was a gift that Airdrie couldn't afford to give.
What looked like a harmless situation soon proved lethal, as Paterson's pass looped over his goalkeeper for Johnston to run in and slot home.
A rattled away side were almost punished a few minutes later when Dillon's header had to be cleared off the line by Scott Agnew. They had to regroup after a torrid opening quarter.
McGill got a rare glimpse of Lanarkshire joy up top on 19 minutes but really should have done better, taking a heavy touch as he looked to be through on goal.
Airdrie were toiling in attack but anything good was coming from recently-crowned PFA League One Player of the Year Easton. The attacking midfielder almost scored on 33 minutes after good play by Callum Smith but couldn't fine the target.
He was much closer moments later as he dragged a shot from outside the box off the post in a big chance for his team.
Lyall Cameron was unfortunate not make it 2-0 after 34 minutes, going on a mazy solo run which evaded Currie's goal by a matter of inches.
More slack play at the back presented the Dundee loanee another opportunity four minutes from half-time but Currie reacted to palm the ball and eventually catch it.
A few Lanarkshire claims for penalties passed by as Murray went down the tunnel at half-time with a big team talk ahead of him after a mixed first half.
Calum Gallagher raced in behind for his manager in search of a leveller 10 minutes after play restarted but after cutting inside, could only trundle an effort wide.
A couple of minutes later and he had another opening but this was also slow and easy to deal with. Montrose soon started to turn the screw and Currie was alert to deal with a few crosses inside his box.
Proceedings had turned into an end-to-end affair and Easton narrowly missed Montrose's bottom corner after great feet outside the box by teammate Paterson. Gallagher then smashed the side-netting with 20 minutes to go as Lanarkshire frustrations grew.
Frizzell was next to roll a shot wide a minute later but Airdrie have it all to do when the return leg rolls around this weekend.
Montrose XI: Fleming, Ballantyne, Webster, Steeves, Dillon, Masson, Whatley (Watson, 83), Cameron (CF Ballantyne, 73) Gardyne, Johnston, Lyons (Milne, 55).
Subs: Callaghan, Watson, Simpson, Rennie, Middleton, McFarlane.
Booked: Johnston.
Airdrie XI: Currie, Paterson, Fordyce, McCabe, Agnew, Gallagher, Easton, Smith, MacDonald, Frizzell, G McGill (Allan, 74).
Subs: Cantley, Kerr, Afolabi, McDonald, Watson, Walker, S McGill, Devenny.
Booked: Frizzell.
Referee: Graham Grainger.
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