Less than six months since his first match in charge of Scottish giants Celtic, Australian manager Ange Postecoglou on Thursday morning (6.45am AEDT) faces one of the greatest matches of his globetrotting managerial career.

Celtic will host Rangers – the other half of Glasgow’s iconic Old Firm – in a match that could prove a watershed moment in the season and wrest back supremacy of one of football’s great rivalries.

Lose, and Celtic would tumble to their longest run of league games without a win over their biggest enemies this century.

Win, and Celtic will leapfrog Rangers into top spot in the league. It is, quite simply, one of the biggest games of the season.

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Celtic dominated the last decade of Scottish football, winning nine-straight Scottish Premierships before Liverpool legend Steven Gerrard conspired to deny a record-breaking tenth consecutive title last season in stunning fashion.

The Hoops finished a humiliating 25 points behind their bitter rivals and failed to reach a single cup final. Manager Neil Lennon was out the door in February, before Rangers sealed the league crown in March – a full two months prior to the end of the season.

Celtic’s squad was a tired shambles, full of players who didn’t wish to be at the club and others that probably didn’t deserve to be.

After months of pursuing top managerial target Eddie Howe in vain – he has since taken over at cash-flushed Newcastle – Celtic turned to Australia’s finest in Postecoglou.

They were, in short, desperate for a miracle.

As former Rangers striker Kris Boyd wrote in The Scottish Sun before the start of this season: “Right now, most would say that Rangers are an absolute certainty for the league. They are huge favourites …”

Postecoglou was written off from the start.

Written off by the Hoops’ faithful, who had watched weeks turn into months as the pursuit of the much-hoped-for Eddie Howe collapsed in a drawn-out calamitous saga. Written off by pundits, too, for a similar reason – Howe boasted a massive reputation from his successful stint in the Premier League, while Postecoglou was plucked from half a world away. One of the great blind spots of European club football is its unwillingness to see past its own history to the unique delights of competitions in the far reaches of the footballing globe. Like Australia or Japan, where Postecoglou had turned Yokohama F. Marinos from also-rans into shock league winners.

For a club in disarray, a manager unwanted by the fans and derided by the pundits could quickly turn into a punching bag – a scapegoat to be punted out the door if Rangers, as expected, ran away with another title.

But if Postecoglou’s lack of reputation was his great weakness, it was also his greatest strength. He did not view Europe as better than Japanese or Australian football. It was simply a different arena in which to prove himself and his unflinching belief in a glittering brand of attacking football.

It would take something radical to turn around the catastrophe of Celtic’s 2020-21 campaign. Postecoglou didn’t take long to prove he was willing to make the bold calls. 12 first-team players departed in his first transfer window, while 10 fresh faces were signed.

It was a sweeping overhaul of the squad, especially impressive since the Australian took charge of his first training session less than a month before their first competitive match.

His tactical overhaul was no less thorough. Postecoglou’s high-intensity style requires extreme focus throughout the entire game, making it both physically and mentally demanding. It is, put simply, not an overnight job, but a long-term restructuring of the thoughts, instincts, and play of those who take to the park.

It comes as little surprise that a new-look squad with a radically different tactical approach struggled for consistency at the start of this season.

Celtic smashed six goals past Dundee then St Mirren in back-to-back home league games. But they failed to qualify for the Champions League proper, and were emphatically crushed in the Europa League including a 4-0 drubbing by Germany’s Bayer Leverkusen.

Then came the first true yardstick of the season. The first Old Firm derby, just four rounds into the league season. Postecoglou travelled across town to Rangers’ Ibrox ground and copped a 1-0 defeat in front of 50,000 fans baying for his blood. If Rangers had taken control of the Old Firm rivalry with their dominant league campaign the year before, the result of this game only affirmed it.

Rangers would lose just one of their 13 league games to start the season. Celtic, by contrast, lost three of their first six – as Postecoglou became the first manager in club history to lose his first three away matches. Celtic were struck down by a host of injuries – a problem Postecoglou continues to face – and slumped to sixth place in the league. The club’s chief executive Dominic McKay, who signed Postecoglou in June, departed just 72 days into his job.

For every promising sign in Postecoglou’s nascent revolution, there were just as many people willing to point out every weakness and failure.

How things have changed.

In those first six league games, Celtic conceded four goals. But in the 17 league games since then, Celtic has conceded just nine goals and has not lost a single game. And for all the focus on Postecoglou’s dazzling attacking styles, the team boasts the best defensive record in the league. Postecoglou guided the team to the Scottish League Cup final and promptly hoisted the first piece of silverware on offer in the season. From no finals the year before, to a trophy within six months. But Postecoglou’s revitalisation of the fallen giants was not complete – not by a long shot.

He had already signed Japanese star Kyogo Furuhashi before the season, drawing on his three-and-a-half years spent in the J.League. But on December 31 he pulled off a staggering transfer heist: Reo Hatate, Yosuke Ideguchi and Daizen Maeda all followed Postecoglou’s path from Japan to Glasgow.

Maeda joined on a loan deal with a compulsory purchase clause come season’s end. But including that fee, the total cost for all four players will amount to less than £10 million.

“If you’re looking at the fees for Maeda and Hatate, Celtic have committed a robbery of a scale it’s impossible to describe,” said Dan Orlowitz, sports writer for the Japan Times.

Furuhashi has quickly become a cult hero at Celtic, scoring 16 times in 26 matches in all competitions. Maeda and Hatate have both scored in the handful of games they have played so far.

Postecoglou, whose Japanese credentials were so disparaged by fans and pundits, turned the narrative on its head and once again turned an apparent weakness into a strength.

THE OLD FIRM

On Thursday morning, the second Old Firm derby will decide top spot in the league.

This time, things are different. Now, Celtic sit just two points behind a faltering Rangers side which has drawn two of their last three league games. It is Celtic who are in form and have a shining trophy in their cabinet to back that up.

But the club’s form is merely a reflection of a key change in the Celtic side since that first meeting of the two clubs in August.

Celtic fullback Josip Juranovic declared this week: “Then we were only playing maybe two weeks together. Now, it’s a little longer and we know each other. It will be a totally different game. We are very strong.

“We are a family on and off the pitch. Team spirit is the most important thing.”

Last year, Postecoglou said that Celtic’s tough start to the season forged a strong bond between the players.

“In the early part of the season, they all had to be really resilient as results and performances were inconsistent. But through that adversity, if you stick together it creates a bond among the group.”

That bond will be tested tomorrow, and the pressure is higher than ever. Victory would mean not just top spot in the league, but would be a major psychological blow to a Rangers team that were widely expected to dominate the league – and the rivalry – again this season.

If that pressure wasn’t enough, Celtic have not won in six league meetings with Rangers – five losses and one draw – a run dating back to 2019. Lose, and they will set a new record for the worst run this century, beating the mark of March 2000, when they also went six games without a win.

But Postecoglou has always thrived under pressure, thrived under the hefty weight of expectations.

Just as the manager this week has played down the pressure of possibly claiming top spot in the league, so too are his players staying calm.

Juranovic said: “Pressure is when a doctor wants to save some lives.

“We are only playing football. We have pressure, but not like that.

“It is not like it is the last game of the championship. It will not decide who is first, or who is second or third.

“We need to play our football from the first minute to the last. After that we will see where we will be.”

Celtic are already miles ahead of where many expected them to be this season. For Postecoglou, this match could prove the doubters wrong yet again – and could prove Celtic are back on top of Scottish football’s great rivalry.