Neil Lennon is looking for an “instant reaction” from his players in tomorrow night's Scottish Communities League Cup quarter-final against St Johnstone following Celtic's historic 2-0 home defeat to Kilmarnock.
Former Celt Cillian Sheridan scored two minutes before the break and midfielder Liam Kelly slammed in the second from the spot just after the hour mark to register Killie's first victory in the east end of Glasgow for a remarkable 57 years.
The Hoops' lacklustre performance was all the more puzzling given their disciplined, battling display against Barcelona in the Nou Camp in midweek, where they only lost the Champions League clash 2-1 to a Jordi Alba goal in the final seconds of stoppage-time.
Celtic remain top of the Clydesdale Bank Premier League but Lennon described his side's performance against Kilmarnock as “unacceptable” and is looking for a big improvement for the visit of the Perth men.
“It was as poor as we have played under my tenureship here and I will be looking for an instant reaction on Tuesday,” said the Parkhead boss.
“You think that after the while they will find their feet and work their way into the game.
“But there was nothing. There were too many touches on the ball and I think the two centre halves of Kilmarnock had one of their easiest games of the season and that is very disappointing.
“I don't remember us working their keeper in the first-half, we had good chances in the second-half but not enough as far as I'm concerned.
“There were times we were passing for the sake of passing and I want better.”
Kilmarnock boss Kenny Shiels was delighted at ending the Hoops hoodoo although he was irked at the suggestion that the champions were not at their best.
“Celtic were up for it,” said the Northern Irishman. “It takes two teams to make a football match. It was a nullification of a quality team. I don't think you can be critical of Celtic.
“There was no way they were physically drained after 11 league games and four days after going to Barcelona.
“The only advantage we had probably, was that so much emotion went into Barcelona it could have drained them and there could have been a hangover but that was the only little area where they were disadvantaged.
“Our boys were brilliant.”
Kilmarnock's unlikely win is another significant addition to Shiels' CV, his side having beaten both halves of the Old Firm last season, most notably Celtic in the Scottish Communities League Cup final at Hampden in March.