The only person who may be more perturbed than Brendan Rodgers at this outcome will be the person in the SPFL who’s presently responsible for compiling the post-split Premiership fixtures.

Had Celtic ticked off the victory which was widely expected here, all they would have required to cross the line in the title race would have been to repeat the trick at home to Kilmarnock on Saturday lunchtime. So much for all of that.

While this unforeseen reversal for Rodgers’ players — a first in 32 games against St Johnstone — won’t loosen their grip on the title, it does throw the league a curve ball in terms of the scheduling of matches after Easter.

The trouble for all concerned is that there’s truly no way of knowing when Celtic will give themselves a shake. Play as poorly they did here and Celtic might force their fans to wait for a while yet.

Trailing from Daniels Balodis’ fourth-minute goal, the visitors had all afternoon to find their composure and the right solution to see off a side which started the day 52 points behind them. 

St Johnstone defender Daniels Balodis rises above Celtic’s defence to head in the only goal

Goalkeeper Andy Fisher comes out to deny Celtic substitute Luke McCowan at McDiarmid Park

For reasons only they could explain, Celtic collectively put in a horror show and were deservedly beaten for the fourth time in the league this season.

For all there was a moderate improvement in their display in the second period, it was never pronounced enough to suggest that a dramatic turnaround was on the cards.

Saints keeper Andy Fisher made some fine saves towards the end of the match yet was hardly overworked.

Frankly, it was hard to escape the notion that on the back of Rangers’ loss to Hibernian the previous day, Celtic felt they simply had to turn up to get the desired outcome.

You had to hand it to Saints, though. With results elsewhere going against them on Saturday, they might well have arrived here with their heads down almost resigned to their fate.

Nothing could have been further from the truth. A first win over Celtic since 2016 keeps them within five points of the pack and very much still in the fight.

While they still evidently have an enormous amount of work to do, if Simo Valakari’s side can replicate the level of spirit and belief they showed here then anyone yet writing them off will do so at their peril.

What a day this was for the Perth club. A few weeks back, this date was pencilled in as Celtic’s title party. Sensing an opportunity to cash in, St Johnstone gave up three stands of their ground.

By time up, it wasn’t just their coffers that had been significantly swollen. Bottom of the table they may still be, but their reserves of self-belief will now also be overflowing.

Rodgers has spoken recently about the need for his side to eradicate slow starts in matches. He wouldn’t have been impressed with what he initially saw here either, yet another sloppy beginning which saw his side trailing inside four minutes.

The visitors could not say they hadn’t been warned. Balodis had already flashed one header narrowly over the top when Jeffrey Schlupp’s error gave Saints a chance to ask another question of their opponents.

Graham Carey’s in-swinging free-kick was whipped in with pace and precision.

Balodis attacked it at the near post and flashed a header beyond Viljami Sinisalo. What a moment for the Latvian international to register his first Saints goal.

The McDiarmid Park pitch looked hard and bumpy yet that alone could not account for the lack of fluency Celtic exhibited in the early exchanges.

You had to tip your hat to Valakari’s side. Folding back into a compact 4-4-2 whenever Celtic had the ball, they gave up little space and stuck doggedly to their tasks.

Their attitude was exemplified by Stephen Duke-McKenna. Daizen Maeda’s angled drive looked set to be tapped home from a matter of inches by Nicolas Kuhn until the Saints winger produced an outstanding goal-line clearance.

Moments later, the same player popped up at the other end, letting fly with a fierce strike. Sinisalo did well to spring to his left and touch the ball away for a corner.

Celtic were devoid of a spark. Their runs were predictable. They wanted too many touches in the final third. Those they did take were invariably clumsy.

Standing with his arms folded on the sidelines, Rodgers was not impressed. Last season, at this same ground, he’d claimed his side’s first-half display caused him to be the angriest he’d ever been in all his time in management. This was certainly no improvement.

Stephen Duke-McKenna steps in to prevent Celtic’s Nicolas Kuhn equalising  from close range 

It said much that his side’s best chance came from an error by Sam Curtis. A wayward back-pass gifted Maeda an opportunity. The Japanese reached the ball first, sidestepped Fisher and rolled the ball towards the target. The Saints keeper recovered in the nick of time and made a goal-saving block.

Gilt-edged chances for Celtic in the opening period were rare. Arne Engels fired straight at Fisher in the opening seconds while Jota — otherwise anonymous — forced the keeper to tip his rising strike over.

Saints might even have been two up at the break. Reo Hatate was fortunate that VAR didn’t penalise him for handball as he fell backwards while trying to defend Carey’s cross.

Adama Sidibeh also forced Sinisalo into a save after he out-jumped Schlupp to win a header.

The only surprise was that Rodgers only made two changes at the break, Greg Taylor replacing Schlupp and Kuhn making way for Yang Hyun-jun.

Celtic restarted with more purpose. Picked out by Engels’ short corner, Hatate smashed the ball against the upright. Unfortunate on that occasion, the midfielder could be given no leeway when he then skied the ball high into the stand from Jota’s cut-back.

For all the pressure increased significantly, Duke-McKenna was inches away from doubling the home’s side lead with a spectacular drive.

Some of Saints’ last-ditch defending was extraordinary. Played in by Hatate, Adam Idah looked set to score with his first touch since stepping off the bench until Zach Mitchell slid in.

Sprung from the bench, James Forrest had a shot blocked before fellow sub Luke McCowan fired the rebound wide. Forrest was also denied by the legs of Fisher after Mitchell’s error before he fired tamely into the keeper’s arms.

In both instances, the veteran winger’s shots lacked conviction. The same could be said of Celtic throughout the afternoon.

There was still time for Fisher to produce one last heroic act when his face blocked McCowan’s strike in stoppage-time.

This result won’t change anything at the top half of the table but it’s certainly shaken things up at the foot.

St Johnstone (4-4-2): Fisher 8.5; Curtis 7, Balodis 8, Mitchell 7, Wright 7 (Steven 67); Griffith 7, Holt 7, Duke-McKenna 8, Carey 7 (Sprangler 67); Kirk 7 (Kimpioka 67), Sidibeh 7 (Clark 67).

Booked: Wright, Holt, Curtis, Mitchell.

Manager: Simo Valakari 8.

Celtic (4-3-3): Sinisalo 6; Johnston 5, Carter-Vickers 5, Trusty 5, Schlupp 4 (Taylor 45); McGregor 5, Engels 5 (McCowan 66), Hatate 5; Kuhn 4 (Yang 45), Maeda 5 (Idah 61), Jota 4 (Forrest 75).

Booked: Taylor, Yang.

Manager: Brendan Rodgers 4.

Referee: David Dickinson 7.

Attendance: 9,090.