Celtic's chance of `winning the domestic treble disappeared as a dreadful display condemned them to a 3-2 defeat at Hampden. St Mirren will now face Hearts in the final on March 17.
The Parkhead side had been overwhelming favourites but have now lost to Kilmarnock, Hearts and St Mirren in their last three visits to Hampden, and won only four of nine visits since Lennon became manager. He described yesterday's as the worst performance of them all, even hinting that it could force him into some rushed transfer activity before the January window closes on Thursday evening.
Lennon was scathing, and particularly irate, about yet another missed penalty by a Celtic player, this time Charlie Mulgrew's effort saved by Craig Samson when the score was 1-1.
"I am bitterly disappointed with that performance," he said. "It was soulless, it lacked intensity, it lacked desire, it lacked will to win. It lacked all the attributes this team has shown over the last six to nine months. I don't know where that performance came from.
"I am sick to death of us missing penalties. Charlie Mulgrew is the best deadball player I've seen for a long time – certainly in Scotland and one of the best in Britain – but I was amazed he sidefooted it. I thought he would have put a bit of power on it. We seem to change our mentality when it comes to penalties."
"Our reaction was poor from the second and third goals onwards," continued Lennon. "There was a lack of discipline in our shape and some of them behaved like spoiled kids out there. I've dealt with it in the dressing room and I'm not going to speak about it again to the players, but I will analyse it.
"The treble is gone and we've only ourselves to blame. Criticism is going to come our way and rightly so. It looks as if it is a mentality thing at Hampden now. That was a pale impersonation of the team that I know. Defensively we were awful, our decision-making was poor and going forward quality was lacking.
"When your team doesn't turn up there is not much you can do, but I don't want to take anything away from St Mirren. It seems to be a bogey ground, this, but that's the worst we've played here. That was awful. I perceive them to be top-class players but maybe I've got it wrong. Maybe I need to look this week in the window and change things - I don't know. None of the players said a word. They had no choice, really, but to listen to me."
Danny Lennon had lost all of his eight previous meetings with Celtic without a goal. Now the St Mirren manager might win the League Cup for the first time in the club's history, and their first trophy since the 1987 Scottish Cup.
"We were inspired by previous Celtic and St Mirren games way back to 1959, we watched videos of some monumental results against them," he said. "The message behind that was to fuel the players' belief that it could be done. What had inspired me was that a fan put a lovely montage on YouTube. In these games you try something different."
Jim Goodwin will be eligible for the final despite fearing a second-half booking would mean he was suspended.