St Mirren's hopes of a second cup final of the season were ended after defeat to Celtic at Barclays Hampden.
Saints fell at the semi-final stage despite a big effort from Craig McLeish's men at the National Stadium. Mikael Mandron's second-half double saw us force extra-time after coming back from 2-0 down.
However, the final period went horribly wrong for the Buddies with Celtic scoring four goals in six minutes in the first-half of extra-time to secure their place in the final.
We had work to do from the off with Celtic taking the lead inside the first minute of the game. A loose touch from stand-in goalkeeper Ryan Mullen - the only change from last weekend's 1-0 loss to Celtic as he replaced the injured Shamal George - saw Celtic's Daizen Maeda press quickly to block the attempted clearance. The ball came off the outstretched leg of the Japanese forward and trundled across the line.
Celtic could have added a second on nine minutes when Arne Engels was afforded too much space 20 yards from goal. The Belgium international had time to set himself before curling off the post.
Saints were dealt an injury blow with Mullen unable to continue after a knock. He was replaced by 17-year-old youth academy goalkeeper Grant Tamosevicius who came on for his first-team debut. The youngster was soon thrust into action, holding a strike from Benjamin Nygren before making a good two-handed stop to deny Maeda a second.
The Buddies' best opportunity came on the half-hour mark and only a big save from Viljami Sinisalo denied us an equaliser. Liam Donnelly rose highest to meet a corner and the Celtic goalkeeper did well to push over the bar. The Celtic goalkeeper was called into action again three minutes later. He clattered a clearance off Killian Phillips and had to be at full stretch to get back and tip it wide.
After a good spell for Saints, it was Celtic who almost doubled their advantage heading into the final 10 minutes of the half. Kieran Tierney's cross when deep to the back post where it met Hyunjun Yang. His header back across goal came crashing off the bar.
Saints could have found themselves level heading into the interval after brilliant pressing from Ayunga saw him deflect a Sinisalo clearance to Mikael Mandron. The forward laid it back into the path of Phillips but he couldn't get the connection required and sclaffed it by the post.
As it was, Celtic would add a second on the stroke of half-time. Ralston lashed high into the net after racing on to Yang's backheel to make it 2-0 leaving Saints with it all to do in the second-half.
But the Buddies would get themselves right back into the match less than 10 minutes after the restart. Declan John swung in a lovely cross from the left side where it met Mandron who guided a brilliant header back across Sinisalo to give us hope.
Saints kept pushing for an equaliser but weren't managing to carve up any real opportunities to get level. With 15 minutes of normal time remaining, McLeish introduced Jayden Richardson, Roland Idowu and Jake Young in place of Allan Campbell, Phillips and Ayunga. Eight minutes later it was Conor McMenamin who came on for Liam Donnelly as we looked to find the goal that would take us to extra-time.
Sinisalo made a double save as the minutes ticked away. His first saw him block with his foot before tipping Mandron's follow-up by the post.
Four additional minutes were confirmed and within the first of those four minutes, Saints drew level. Miguel Freckleton was quickest to react to a flick-on from a Celtic throw-in. He knocked the ball on to Young who hooked the ball over the top for Mandron. The forward outpaced Benjamin Arthur and lashed a brilliant finish beyond Sinisalo to complete the comeback and ensure another 30 minutes of time at Hampden.
But any hopes of Saints reaching the final in May were extinguished in a tough six minute spell where Celtic added four goals. Kelechi Iheanacho scored twice either side of a Luke McCowan strike while Benjamin Nygren netted a sixth.
Full-Time: Celtic 6-2 St Mirren (After extra-time)
St Mirren: Mullen (Tamosevicius 15), Donnelly (McMenamin 82), Gogic, Freckleton, O'Hara (c), Phillips (Idowu 74), Devaney, Campbell (Richardson 74), John (Tanser 106), Mandron, Ayunga (Young 74)
Subs: Calvin, Douglas, Etete
Celtic: Sinisalo, Ralston, Trusty, Arthur (Murray 91), Tierney (Saracchi 83), McGregor (c) (Oxlade-Chamberlain 73), Engels (McCowan 73), Nygren, Tounekti (Forrest 61), Yang (Iheanacho 83), Maeda
Subs: Doohan, Hatate, Adamu
Referee: Matthew MacDermid
AR1: Calum Spence
AR2: David Roome
Fourth Official: Ryan Lee
VAR: Kevin Clancy
