Just six months on, he has become an icon for the Celtic support, the manager's name ringing out at Hampden in the wake of the club's dramatic League Cup triumph on Sunday.

Postecoglou has calmed the chaos, overhauled the squad and delivered a trophy at the first attempt. The 2-1 final win over Hibernian mirrored his tenure as Celtic, having fallen behind, roared back from adversity.

"I'm usually pretty good but I'm struggling to find the words this time," said the 56-year-old.

"I can't guarantee success, but I wanted to give the fans hope and they saw that from the first day. It hasn't been smooth, we have had ups and downs, but I think they saw hope in us.

"The players are so resilient. I'm so happy they have had their rewards for it today."

Troubled start at club in transition

Postecoglou wasn't even first choice for the manager's job, with Celtic hastily beating a path to his door after a lengthy and doomed pursuit of former Bournemouth boss Eddie Howe.

Postecoglou has won titles in his homeland and Japan, where he was prised from Yokohama Marinos, as well as managing Australia at a World Cup.

But he has had to prove himself all over again in his first job in European football at a club that lurched from four years of constant success - an unprecedented quadruple treble - to a first season without a trophy in more than a decade.

It's not hyperbole to suggest Postecoglou inherited a mess as successor to Neil Lennon. Celtic finished 25 points behind Rangers last season and he soon lost key players Odsonne Edouard, Kristoffer Ajer and Ryan Christie to English clubs.

His first games in charge emphasised the scale of the rebuild required as Celtic - fielding a defence with an average age of 21- were dumped out of Champions League qualifying by Denmark's Midtjylland then lost their Scottish Premiership opener against Hearts.

New signings, lots of them, were needed, and Postecoglou showed he wasn't content to be a 'yes man' to the board as he repeatedly called for reinforcements to arrive more quickly.

Despite some promising signs - such as the 6-0 destruction of Dundee - Celtic made their worst start to a league season in 23 years, collecting just nine points from the opening six games.

Signings flourish in silver-plated revival

Yet Postecoglou stuck rigidly to his principles - high-intensity, high-risk attacking football - and the fans quickly bought into his vision.

While defensive vulnerabilities remain - as evidenced by Paul Hanlon's set-piece opener for Hibs in the final - Celtic are a thrilling force going forward.

The League Cup triumph was their seventh consecutive victory. From the start of October, they have played 17 games across all competitions, winning 15, with the sole defeat coming against German side Bayer Leverkusen in the Europa League.

They have risen from sixth in the Premiership to second, seven points behind Rangers, with the Old Firm derby looming at Celtic Park on 2 January.

The majority of Postecoglou's key signings have flourished. Kyogo Furuhashi made it 16 goals for the season with his match-winning Hampden double. Former England goalkeeper Joe Hart contributed a huge late save and has rebuilt his reputation in Glasgow.

Winger Jota, injured for the final, centre-back and fellow loanee Cameron Carter-Vickers, and full-back Josip Juranovic have all impressed.

Existing players have thrived too in the new era, particularly midfielder Callum McGregor, who took over as captain from the departed Scott Brown.

There's a mutual respect that underpins Celtic under Postecoglou, who says: "You come to work with footballers but the gold comes from working with people and these players are special people.

"I have a special relationship with all of them. The ones I brought in, I take responsibility for them."

McGregor was quick to praise the manager as he added: "He demands of us every single day and asks us the team we want to be.

"For this group of players to come together in the summer and achieve a trophy at the first time of asking is special. We wanted to get last season out of our system and get the club back to success.

"We keep pushing and just want more success now."