St Mirren were denied a Premier Sports Cup quarter final spot in the cruellest possible fashion after being edged out on penalties.
In a close-run first 45 minutes St Mirren were eventually punished for spurning two superb chances, with Greg Kiltie and Eamonn Brophy both guilty of poor finishes with the goal at their mercy.
Alan Forrest showed the former Killie pair how it's done, calmly curling home the opener just before the half-time break to give the hosts the lead.
The second half saw very few chances of note, with the Buddies increasingly disjointed and the strikers finding themselves isolated up front.
The Paisley side still managed to take the tie to extra-time when Conor McCarthy beat Livi's offside trap from a free-kick to stab home a vital leveller.
There was controversy in the second half of extra-time when Nicky Devlin's close-range effort had Livingston's players screaming the ball had crossed the line, with the linesman deeming Saints keeper Jak Alnwick to have just kept it out.
The tie was eventually settled on penalties, with Jason Holt netting his side's sixth spot kick and Kyle McAllister's pivotal final effort pushed onto the bar.
In a rematch of January's semi-final clash between the pair in the same competition, which Livingston narrowly won 1-0 thanks to Scott Robinson's early goal, Jim Goodwin was forced into one change from the Buddies' 2-1 defeat at the hands of Hearts.
Ethan Erhahon came into midfield in place of Alan Power, with Eamonn Brophy and Curtis Main again the preferred strike partnership up front.
There was an early scare for the noisy travelling support as Charles Dunne failed to deal with a simple Livi long ball. Thankfully for the Saints he recovered in time to deal with the danger at the second attempt.
The hosts started the game on the front foot, with Scott Pittman allowed to stroll through the heart of the Saints midfield before unleashing a powerful low strike which Jak Alnwick held well.
Joe Shaughnessy was the unlikely provider of St Mirren's first serious chance, with his pinpoint long cross unleashing Scott Tanser on the left flank. He drifted inside before firing wide of Max Stryjek's left hand post.
Livi didn't take long to get back in control of the tie and Odin Bailey's curling strike from the edge of the box flew just inches past the post with Jak Alnwick rooted to the spot.
As is often customary in Livingston the match was more of a war of attrition in the opening stages, with passing football very much at a premium.
On the 20 minute mark Saints really should have opened the scoring when Jamie McGrath released Tanser on the wing.
His cross was cleared only as far as Greg Kiltie, who shot far too close to Stryjek from just ten yards out. The keeper parried away the strike with the ball falling back to Tanser, who found Brophy on the edge of the box. The ex-Killie striker's low shot was easily dealt with by the Livi goalkeeper.
There was a serious cause for concern for the Buddies when Dunne, who has spent much of the last two years on the treatment table, went down injured around the half hour mark.
He was replaced by Conor McCarthy, with the decision to risk the former Motherwell centre back on Livingston's artificial pitch appearing to backfire.
Brophy's ambitious attempt at an overhead kick from a Marcus Fraser cross sailed harmlessly wide of the post, with McGrath skinning his man on the edge of box shortly after and producing an excellent cross that Richard Tait headed narrowly wide.
St Mirren were made to pay for wasting their clear cut chances five minutes before the break as Bruce Anderson's long pass released Forrest on the break.
He cut inside the retreating Buddies defence before curling past Alnwick into the bottom right corner to break the deadlock.
The Paisley side had the perfect opportunity to level just before the break when Brophy was released through one-on-one with Stryjek, despite appearing to initially be in an offside position.
The linesman kept his flag down, but a combination of a tremendous save and unconvincing finish saw the hosts maintain their one goal advantage at the break.
Saints skipper Joe Shaughnessy went into the book early in the second half after doing his best Giorgio Chiellini impression and hauling back Pittman as he raced through on goal.
Ayo Obileye then headed over the bar from a Forrest corner as the Lions looked to quickly double their advantage in the tie.
St Mirren were struggling to gel in midfield, with Kiltie overcooking a simple pass in the final third as the Livi defence remained largely unchallenged.
Goodwin made a double change with half an hour left on the clock to try and breathe some life into his toiling side, with youngsters Jay Henderson and Cammy MacPherson replacing Tait and Kiltie.
Shaughnessy pulled off a superb last-ditch tackle to halt Anderson as he dribbled his way into the box, with Livi looking the more likely to trouble the scoresheet as the game progressed.
Playmaker Kyle McAllister entered the fray with quarter of an hour to play, replacing Fraser as the Buddies desperately sought an equaliser.
With less than ten minutes to go St Mirren found themselves level. Livingston tried to play offside from a free-kick but got it horribly wrong, allowing Conor McCarthy all the time in the world to slot home from close range.
The Buddies almost completed the turnaround just two minutes later as Main slotted home at the second attempt from inside the box, with only the linesman's flag denying him a winner in normal time.
Pittman dragged a shot narrowly wide from the edge of the box as the clock ticked down, before Main blasted one last chance over the bar after good work on the wing.
The Buddies returned for extra-time with Lee Erwin replacing Brophy, who was clearly struggling with an injury towards the end of the second half.
Erwin saw a shot blocked by former Buddie Sean Kelly as St Mirren tried to fashion a winner, with Jack Hamilton heading straight at Alnwick at the other end.
Erwin was doing his absolute best to spark a winner for his side, producing a superb cross from the left wing which Main couldn't quite connect with.
Livi thought they'd found a winner in the second half of extra time when Ayo Obileye's header hit the post and rebounded back to Nicky Devlin. His low shot was saved by Alnwick, with the hosts adamant the ball had crossed over the line.
The Buddies ended the second half of extra-time with just ten men, with Tanser forced off injured and Goodwin having already used all five of his subs.
They hung on to force the tie to penalties, with McGrath, Erwin and Shaughnessy all netting.
Main dragged his effort wide, while MacPherson saw his effort saved. Alnwick managed to save from Jacobs and Sibbald, but as the spot kicks went to sudden death Jason Holt slammed home leaving McAllister needing to find the net.
His shot was saved agonisingly onto the bar, with the Lions finally sealing their place in the quarter finals.
