Darren Young's penalty sent Dunfermline Athletic to their first CIS Insurance Cup final since 1991 at the expense of fellow SPL strugglers Livingston.
Livi had started the brighter, with some last-ditch Pars defending preventing an opener and Paul Dalglish testing goalkeeper Allan McGregor.
Young fired the winner from the spot after Greg Strong felled Mark Burchill.
Noel Hunt struck the Livi post before Dunfermline comfortably held out for victory after the break.
Dunfermline, one point ahead of Livingston at the bottom of the Scottish Premier League, now await the winner of next Wednesday's semi-final between Celtic and Motherwell.
The Pars went into the game having lost the services of influential midfielder Lee Makel and the versatile Andy Tod, with striker Bartosz Tarachulski relegated to the bench.
Simon Donnelly, Gary Mason and Craig Wilson took their places after the Pars' 3-1 league defeat by Hibernian.
Livingston player-boss Paul Lambert had resisted the temptation to field himself and kept faith with the starting 11 praised despite losing 4-1 to Rangers at the weekend.
And the West Lothian side looked confident early on when Dalglish made room for himself and fired a shot from 20 yards that was heading on target until Greg Shields deflected it clear.
David McNamee sent a header a few yards wide and a drive past the far post.
And fellow defender Dave Mackay's shot was deflected just wide as Lambert's men started the brighter.
Another powerful, spinning Dalglish effort almost deceived Allan McGregor, but the Pars goalkeeper parried the ball clear.
But Dunfermline gradually took control of midfield and the match.
Burchill was denied twice by last ditch tackles on the edge of the box, the Dunfermline striker's second effort being deflected just over.
But, when Strong pulled down Burchill after the striker sent the ball through his legs inside the box, Young put the Fifers ahead from the spot.
Hunt fired against the outside of the post from an acute angle after jinking into the box as the Pars came close to extending their lead.
Dunfermline appeared to adopt a more defensive philosophy after the break and almost paid for that when a Steve Hislop was deflected wide.
Tarachulski fired straight at Livi goalkeeper Roddy McKenzie when Donnelly was clear and waiting for the return pass after the former Celtic man had set up the substitute.
And Dunfermline survived late pressure to win.
Dunfermline: McGregor, McCunnie, Shields, Scott Wilson, Zambernardi, Craig Wilson (Ross 87), Mason, Darren Young, Donnelly, Burchill (Labonte 83), Hunt (Tarachulski 70).
Subs Not Used: Halliwell, Thomson.
Goal: Darren Young 37 pen.
Livingston: McKenzie, McNamee (Walker 76), Pinxten, Strong, Mackay, Brittain, Vincze (Dair 53), Tierney, Hoolahan, Hislop (Snodgrass 64), Dalglish.
Subs Not Used: Roy, Dorado.
Ref: Dougie McDonald