Di Giacomo scored the only goal of the tie in the third minute.
Airdrie United booked their place in the final of the ALBA Challenge Cup with a narrow win over Partick Thistle.
Paul Di Giacomo scored the only goal of the tie in the third minute, striking low past keeper Craig Hinchcliffe, but missed a penalty in the second half.
Thistle never really established a foothold on the game, despite late efforts from Simon Donnelly and Kevin McKinlay after the break.
Airdrie will now face Ross County or Morton in the final on 16 November.
Airdrie were first on the score sheet after only three minutes when Di Giacomo picked up a stray ball on the halfway line and made a direct run into the Thistle penalty area before striking low past Hinchcliffe.
Thistle's first attempt on goal came from a free-kick that ended up bobbling around inside the Airdrie penalty area until Darren Smith made the block and cleared to safety.
With 22 minutes played, a shot from Thistle's David Rowson was deflected out for a corner and the home side's claims for handball were waved away.
On the half-hour mark, Airdrie's Simon Lynch broke free on the right and powered into the Thistle box but a well-timed tackle by John Robertson forced the strike wide.
Following the break, Thistle continued to look in disarray as Airdrie pressed to double their lead.
Airdrie's Joe Cardle directed in a header from the six-yard line but Thistle defender Paul Paton managed to control the ball with his chest and made a nervy clearance.
Moments later, Simon Donnelly leapt above the Airdrie defence at the back post but fired his header wide of the mark and managed to injure himself in the process.
On the hour mark, Kevin McKinlay thundered in a powerful drive from a corner that struck the Airdrie crossbar and seemed to boost the home support.
With 20 minutes left on the clock, Thistle made a series of frenzied attacks on the Airdrie goal but could not find a way through.
Thistle's Liam Buchannan lined up a shot at goal from the edge of the penalty area but his feeble effort bobbled through the crowded defence and keeper Stephen Robertson easily gathered.
As time ticked out, Donnelly set up a shot from close range but David Nixon pounced and blocked with a deft tackle.
Less than a minute later, Robertson pulled off a fantastic save to deny McKinlay when the former Ross County man attempted to nod in from three yards out.
Di Giacomo stepped up to take a penalty kick in the dying minutes of the match but Hinchcliffe managed to block it with his legs and kept Thistle in the game.
A late flick-on from McKinlay failed to pick up enough momentum and Robertson gathered comfortably for Airdrie to march on to the final.
Partick Thistle assistant manager Gerry Britton:
"We turned up in the second half, that was the difference.
"In the first half, Airdrie caught us cold with the goal early doors.
"We're very disappointed with the way we played. Any second balls, Airdrie were first to them, and that was the difference in the first half.
"Second half, we were a lot better in that department and created a few chances, but we still didn't do enough to win the game."
Airdrie manager Kenny Black:
"I thought they did great. I've got to be honest, they were due a little result like that and I thought they gave me everything.
"They're a determined, honest bunch - they'll make mistakes, but my job is to make sure the mistakes become fewer and fewer.
"Airdrie being Airdrie, we made it hard for ourselves. After the first half I thought we were the better team, but Thistle were the better team in the second half.
"The penalty might have made it easier for us, but that wouldn't have been Airdrie if we had."
Partick Thistle: Hinchcliffe, Storey, John Robertson, Maxwell, Twaddle, Turner, Rowson (Chaplain 81), McKeown (Paton 46), McKinlay, Donnelly, Roberts (Buchanan 61). Subs Not Used: Lennon, Murray.
Booked: Rowson, McKinlay.
Airdrie Utd: Robertson, Bobby Donnelly, McKenna, Nixon, Lovering, McDougall (Brown 72), Darren Smith, McLaughlin, Cardle, Di Giacomo, Lynch (Noble 79). Subs Not Used: Hazley, Watt, Hollis.
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