St Mirren are heading to Hampden after a penalty shoot-out win over Kilmarnock.
The match went the distance after the sides couldn't be separated after 120 minutes of pulsating action at Rugby Park. Mikael Mandron and Jayden Richardson twice had Saints ahead with a pair of fine finishes, but Killie equalised twice through Robbie Deas and Bruce Anderson to take the game to extra-time.
Saints were perfect from the spot with Richard King, Roland Idowu, Liam Donnelly, on his debut, Dan Nlundulu and Malik Dijksteel all netting, while Shamal George saved from Kyle Magennis to send the Buddies into the last four.
Both sides made one change to their previous fixture with King coming in from the start in place of the injured Marcus Fraser for Saints. Ex-Buddie Greg Kiltie started for the hosts with Rory McKenzie dropping to the bench.
In what would prove to be a cup classic, a frantic start to the match saw Jonah Ayunga reach a cross from Killian Phillips at the far post and fire into the side net with only a minute played, while Kiltie stung the palms of Shamal George a little over 30 seconds later with a low shot from 20 yards.
Saints looked bright in the opening stages with Richardson sending a low ball across the face of the box which was begging for anyone in black and red to get on the end of. On eight minutes, Mandron forced a brilliant save from Kilmarnock goalkeeper Max Stryjek. The forward's low drive looked destined for the bottom corner but for the Killie stopper to push wide at full stretch. Mandron did well two minutes later to get his head on the end of a Richardson cross but he flashed the header wide.
Kilmarnock should have taken the lead on 12 minutes when Marcus Dackers robbed the ball from King near the Saints box. The forward played the ball to his strike partner Djenairo Daniels who teed up Kiltie who had arrived in area. He looked primed to fire the hosts ahead though curled the effort by the post.
Kiltie was Killie's out ball and his running down the left saw him draw fouls from both Phillips and Richardson with the Saints pair both shown yellows.
Mandron, who netted in last weekend's win over Falkirk and registered six goal contributions in the Premier Sports Cup prior to tonight, gave Saints the lead on 25 minutes. The forward brilliantly took down a pass from Richardson before lifting the ball over Lewis Mayo and running on to the ball. Mandron worked his way into the box and lashed beyond Stryjek to the delight of the 2,200 plus travelling support.
Mikael Mandron opens the scoring against Kilmarnock (Image: Allan Picken)
Robbie Deas drew Kilmarnock level heading into the final minutes of the half. A free-kick from Dominic Thompson was met by the Killie captain and he thumped home to make it 1-1.
Saints came agonisingly close to taking the lead less than 10 minutes after the restart. It was excellent work from Miguel Freckleton down the left with the ball across falling to Phillips. The Irishman struck it well but an unbelievable reaction stop from Stryjek denied what looked destined to be a second for Saints.
The Buddies would, however, hit the front again with Richardson scoring a goal of the season contender just before the hour mark. Keanu Baccus' cross was headed out by Deas only as far as Richardson who, 20 yards from goal, brought it down on his chest and volleyed into the top left-hand corner. A truly stunning strike that gave Saints a well deserved lead for the second time.
Stephen Robinson's men had the bit between their teeth and almost added a third just a minute after going ahead when Ayunga robbed the ball in the middle of the park and drove forward. The striker teed up Baccus on the overlap but the Australian's shot was blocked. It would spin to Mandron who found Ayunga and the Kenyan was denied by Stryjek as the Killie 'keeper tipped over.
Freckleton made a brilliant defensive block on 64 minutes as Kilmarnock chased an equaliser, while Declan John came close to scoring in the second game in a row when he clipped a free-kick inches over the bar from the edge of the area.
Saints looked the more likely to score again and put the game out of sight. Mandron brilliantly fashioned some space to work his way into the box and get a strike away on goal. But he shot straight at Stryjek.
Kilmarnock would get themselves back on terms with five minutes of normal time remaining. King was judged by referee David Dickinson to have felled substitute Marley Watkins and that allowed Anderson to fire home from 12 yards to take the game to extra-time.
30 minutes of tentative extra-time couldn't separate the sides and that meant the game would be decided by spot kicks. King, Idowu, Donnelly and Nlundulu netted and when George saved Magennis' penalty that allowed Dijksteel to score the winning penalty as he did against Hearts in the previous round.
The Buddies become the first side to book their place in the last four of the competition and will have a trip to Hampden to look forward to on the first weekend in November.
Full-Time: Kilmarnock 2-2 St Mirren (St Mirren win 5-3 on penalties)
St Mirren: George, King, Gogic, Freckleton, Richardson (McMenamin 97), Phillips, Baccus (Idowu 89), O'Hara (c) (Donnelly 75), John, Ayunga (Dijksteel 90), Mandron (Nlundulu 97)
Subs: Mullen, Tanser, Calvin, Mooney
Kilmarnock: Stryjek, Brown (Magennis 84), Mayo, Stanger (Williams 109), Deas (c) (Brannan 83), Thompson, Polworth (Watkins 79), Watson, Kiltie (McKenzie 91), Dackers, Daniels (Anderson 60)
Subs: Beach, Thomson, Schilte-Brown
Referee: David Dickinson
Assistant Referee: Calum Spence
Assistant Referee: Ross Nelson
Fourth Official: Dan McFarlane
Attendance: 7,192 (2,252 St Mirren supporters)