Airdrie will face Queen’s Park in a promotion showdown after edging an epic play-off semi-final against Montrose, with the Diamonds winning by the odd goal in 11 over two legs.

In a match that will live long in the memory, the Diamonds showed the astonishing determination which has endeared them to the New Broomfield faithful this season, coming back to win after extra-time when they looked to be dead and buried.

A hat-trick from Callum Smith and goals from Calum Gallagher, Jon Afolabi and Gabby McGill will go down as the stats that count, but every man in a Diamonds shirt went above and beyond in their efforts to turn around this incredible tie.

Ian Murray made one change to the side which had lost 1-0 at Links Park on Tuesday evening, Scott McGill replacing namesake Gabby.

Montrose boss Stewart Petrie brought in Cammy F Ballantyne and Lewis Milne as the Gable Endies sought to build on their narrow lead.

A 2,000 strong crowd roared the teams onto the pitch, and the Diamonds made a bright start, Smith latching onto Rhys McCabe’s long throw inside the first minute, but the close attentions of the visiting defence saw the striker’s touch go behind.

Kyle MacDonald had an effort charged down after a clever touch in the sixth minute, and Gallagher had Allan Fleming scrambling to tip a long-range effort wide two minutes later.

As Montrose came into the match it took some good defending from Adam Frizzell to dispossess Lyall Cameron on the edge of the box after good work by Craig Johnston in the 10th minute, but disaster struck for the Diamonds two minutes later.

Cammy Ballantyne’s touch on the left made space for the defender to swing in a cross, and Cammy F Ballantyne leapt between two defenders to nod past Max Currie from close range.

Calum Gallagher tried to place one in the top corner on 20 minutes, but the striker was turning towards goal and the shot drifted wide.

With the Diamonds knowing they needed two goals to force extra-time, things went from bad to worse for Ian Murray’s men on 26 minutes. The goal was similar to the first, Lewis Milne crossing from the left flank, but this time the ball dropped at the feet of Ballantyne, who had the easiest of tasks to poke home.

With only 30 minutes played, Ian Murray rolled the dice with a double substitution as Gabby McGill and Craig Watson replaced MacDonald and Scott McGill.

Three minutes later Fleming was in action again, diving to save well from Smith after the striker had forced his way through the centre of the Montrose defence. The striker then nodded Watson’s diagonal ball wide of the target.

Dylan Easton had a shot deflected over on 36 minutes, and McGill fired over four minutes later.

Milne’s shot took a touch on the way over three minutes before the interval, and Watson saw a header blocked on the line from a stoppage-time Scott Agnew corner.

Airdrie made further attacking changes at half-time, Jordan Allan replacing Brody Paterson as the Diamonds attempted to claw back a three-goal deficit.

A 52nd-minute Easton ball across the face of goal found no takers, and less than a minute later the midfielder almost pulled one back in outrageous fashion as he sent a dipping 30-yard strike crashing off the bar.

Airdrie did get their goal a minute later, Easton and Frizzell combining to feed Smith, who skipped past a couple of challenges before unleashing a tremendous right-footed finish into the bottom corner from the edge of the box.

Now back to two ahead, Montrose slowed the game down with substitutions and tactical fouls, but Seán Dillon and Fleming both had to be at their best to clear from Gallagher and McGill respectively just after the hour-mark.

Airdrie’s momentum looked to have been killed completely on 69 minutes as Montrose grabbed their third on the break, a quick passing move allowing Johnston to pick out Milne at the back post, and the midfielder steadied himself before scooping the ball past Currie.

Jon Afolabi replaced Scott Agnew, and a minute after Montrose had looked like ending the tie, the big Irish striker had played a vital part in Smith’s second goal. McCabe’s ball from midfield was worked to the Celtic loanee, who played a square pass across the box for Smith to slam home from the corner of the six-yard box.

Airdrie almost levelled straight away, but Fleming produced another top save to turn Callum Fordyce’s header round the post.

The Diamonds tails were up, and the sizeable support sensed that something amazing could happen as they roared their side on - and on 76 minutes the imperious Smith grabbed his hat-trick. McCabe’s ball over the top landed perfectly for the striker, who took a touch and swept beyond Fleming to level the scores in the match and bring the Diamonds within touching distance of their opponents.

Montrose managed to keep out a near-post Gallagher effort and a McCabe throw as a chaotic match moved into the final ten minutes.

Airdrie could smell blood, and Easton was denied by Fleming on 82 minutes before Milne went close at the other end, but with three minutes remaining the tie was level. Fleming charged to the edge of his box but failed to hold a high ball, and as Afolabi, McGill and Smith all tried to return the ball into the danger area, it eventually fell for Gallagher who was deadly from six yards.

As the songs rang around the Excelsior Stadium, the Diamonds almost won it in stoppage time as Easton saw an angled strike hacked off the line, but the whistle went and extra time loomed.

After a worrying stoppage when McCabe collided with the post in the process of making a last-ditch clearance, the game opened up with Fordyce making a superb challenge on Montrose sub Blair Lyons.

The Diamonds skipper was denied by a fine Dillon challenge at the other end, and Easton had a shot blocked after working space in the box.

With 105 minutes on the clock, Airdrie went ahead for the first time in the tie. Allan showed great strength to hold up Watson’s long ball, knocking it down for Afolabi who had time to pick his spot with a tremendous finish.

Fleming held a 111th-minute Easton shot as the Diamonds’ fitness began to prove telling, and Dillon was lucky to escape with a yellow after a last-man foul on Afolabi three minutes later.

McGill was unlucky with a heavy first touch as he raced onto Frizzell’s through-ball with three minutes remaining, but the English striker made amends in the final minute, rifling Afolabi’s pass into the roof of the net from a tight angle to make it 6-3 on the day and 6-4 on aggregate.

There was time for Montrose to grab another in stoppage time, Paul Watson nodding a cross from the right into the path of Martin Rennie who placed a fine header out of Currie’s reach.

There was no further action as referee Alan Newlands called time on an unbelievable two hours of football, with the Diamonds progressing to next week’s final against Queen’s Park