David Martindale acclaimed Livingston's answer to Sergio Aguero - "wee wasp" Scott Robinson - for firing the club into just a second major cup final.
Robinson's 10th-minute header saw off stubborn St Mirren to ensure Livingston return to Hampden on 28 February to face St Johnstone in the Scottish League Cup showpiece.
Victory extended Martindale's unbeaten start as head coach to 11 games.
"He's a wasp, wee Aguero," Martindale said of match-winner Robinson.
"I thought he was absolutely fantastic, his link-up play, and he took his goal really well."
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Robinson pounced to nod home the rebound after defender Efe Ambrose's close-range header cannoned back off the crossbar.
"He's lucky we've won," Martindale joked of Ambrose's miss. "At Celtic Park he nearly hit the ball over the stand from an open goal. At least he hit the bar and kept it alive this time!"
Livingston had to survive a penalty scare - Nicky Devlin went unpunished for a late challenge on St Mirren's Joe Shaughnessy - and heavy second-half pressure to reach a major final for the first time since lifting the trophy in 2004.
"I'm absolutely thrilled for the community, staff, the board, everyone connected with the club," added Martindale.
"I don't think anyone remembers how you get to the final, because at times it wasn't pretty, but who cares? I think the ball is away to the local hospital. It was two honest teams giving it everything."
Martindale admits he could not have dreamed of a better start in the job, having followed up an eight-game winning run with successive draws against Celtic before Sunday's semi-final triumph.
"Even if you had asked me when I took over as caretaker manager, you'd have probably said it would be great to win the next two or three games," he said.
"But I never thought I would be sitting here 11 games undefeated and going into the League Cup final. It's a collective effort. Obviously I played a big part in that but I'm a small cog in a big wheel."