Kilmarnock’s last gasp winner at Rugby Park added to Celtic’s growing sense of sobriety.

Drunk on the success of the glory seasons under Brendan Rodgers, these opening weeks of the season have felt like a long, slow hangover.

The summer started with the confetti and cheers of an open-top bus parade, silverware and grins glinting against the sunshine. As the nights start to draw in, Celtic are fearing their own winter of discontent.

It might be too early to sound alarm bells just yet – the season remains in its infancy after all – but the alacrity with which Celtic have gone from an air of infallibility to a team who look tentative, pedestrian and critically vulnerable is staggering.

It cannot all come down to a poor transfer window.

Since his arrival at the helm of the club two years past in June, Brendan Rodgers has clocked up all manner of stats; the fabled invincibles of his inaugural season, the back-to-back trebles, the record goal-scoring stats.

Yesterday saw a dive into the record books for a much bleaker comparison.

This season Rodgers’ side have shipped eight points in their opening six league games. To frame that within the accomplishments of their own achievements, Celtic lost eight points in the entirety of Rodgers first season at the club.

Indeed, it is a leaf through the stats all the way back to Dr Jo Venglos’ time in season ’98-99 to draw a parallel to the last time Celtic’s opening start to a campaign was as slipshod as this.

Currently six points off of league leaders Hearts, Celtic seem like a team short on many levels but, crucially, on confidence. When was the last time the Parkhead side lost a game with the final kick of the ball?

Once upon a time Kilmarnock were Celtic’s bogey team; under Steve Clarke the Rugby Park side look capable of haunting Celtic again.

Rodgers has yet to have the beating of Clarke in Scotland with the Kilmarnock manager now overseeing two wins and two draws against the Parkhead side.

How St Johnstone must scent blood.

The Perthshire side will host Celtic on Wednesday night in the Betfred League Cup, a game that now carries all kinds of significance.

The League Cup was the first domestic trophy that Rodgers won at Celtic. It is not the first one he would like to lose having retained it at every time of asking since getting his hands on it.

Celtic look like a team bereft of energy, creativity and ideas.

Interestingly, they had gone into yesterday’s game on the back of five consecutive clean sheets.

The ultimate problem seems to be not so much that they can fall asleep and lose concentration as they did against Kilmarnock but that they can dominate and control possession without creating genuine chances, without carving teams open the way they once were.

Where Celtic were once devastating from middle to front they have become insipid and predictable.

Even the goal that came from Leigh Griffiths in the opening period that gave Celtic the lead against Kilmarnock came through a slapstick mistake from the Rugby Park side rather than a move that opened the Ayrshire side up.

Former Rangers defender Kirk Broadfoot awkwardly sliced a Kieran Tierney cross which then bounced to Greg Taylor in the box. Caught off guard, Taylor’s attempted clearance went onto the join of the crossbar and post with Griffiths and Scott Sinclair falling over themselves to ensure a head went onto the rebound and got the ball over the line.

Even from then on as Celtic controlled much of possession, they could not turn the screw and see the game out.

There was a save from Jamie MacDonald to repel a Ryan Christie effort while Dedryck Boyata looked dangerous from set pieces but there was not a siege laid on Kilmarnock’s goal the way that was the hallmark of Rodgers’ teams.

Jack Hendry had been a late call-up to the starting XI following the flare-up of an old achilles injury to Filip Benkovic in the warm-up.

That added to the sense of changes as Rodgers shuffled things in the aftermath of Thursday night’s win over Rosenborg but there was no sense of energy or impetus within the Parkhead side.

There was a debut for former Kilmarnock midfielder Youssouf Mulumbu but he looked off the pace, inevitable perhaps given his months without a club this summer.

Kilmarnock’s leveller in the second period came as Celtic dithered, with Chris Burke lashing an effort into the bottom right-hand corner from the edge of the box.

Described as “scrappy” by Rodgers there were few other genuine chances for either team.

Celtic made the changes in the second period as they look to take all three points with Odsonne Edouard introduced while Lewis Morgan and Callum McGregor were also brought off the bench.

The sting in the tale, though, came from Kilmarnock. With the game in the third minute of stoppage time, Burke’s corner fell in between Celtic’s two central defenders for Stuart Findlay to head home the winner.

Between now and Wednesday’s trip to Perth, Celtic need to rediscover something of their mojo.