"Aaron, Aaron Mooy! Aaron, Aaron Mooy!"

It's the newest popular ditty cascading down from the stands from the Celtic faithful in homage to, well, Aaron Mooy.

By his own admission, the Aussie was not at all familiar with the strains of Boney M's classic Daddy Cool - coach Harry Kewell can certainly keep him right on that front.

Mooy had better get used to hearing his name shouted from the rooftops in Glasgow's east end though. It's fair to say he has found a football Paradise there under Ange Postecoglou.

The former Australia manager knew exactly what he was doing when he brought Mooy to Celtic for free. I'll state the second part of that sentence again: Aaron Mooy, for nothing.

The 32-year-old was viewed as a somewhat underwhelming signing by some of the supporters in the summer. Eyebrows were raised. Trust the manager, trust the process and all that though. His World Cup performances for the Socceroos certainly captured the attention just as wily Postecoglou knew they would.

Mooy well and truly arrived as a Celt the night he bagged a brace at Easter Road in the 4-0 demolition of Hibs on December 28.

It was the same night that song was heard for the first time and his display prompted Postecoglou to say this: "With Aaron, again, it was just about getting him fit. It’s hard for people to sort of conceptualise but he had played probably two games of football in six months before we signed him.

"So I knew that when we signed him it was going to take a little bit of time to get to the fitness levels we need him to be and he needs to be, but at the same time, I knew that when it happened he’s got such a good engine. His ability to run, his quality, would eventually shine through.”

When he first rocked up at Celtic Park, Mooy to the naked eye looked slow, ponderous, unfit and unconvincing. When you bear in mind that Mooy had arrived in a new/old country - as he had previously played for St Mirren - and he was embarking on a new career at a club where the demands are incessant then you can cut him some major slack for getting off to a sluggish start. Postecoglou's faith in him never wavered though, not one iota.

The World Cup finals in Qatar have helped turn the Aussie into a machine capable of running the Hoops midfield. So much so that he was at it again as his slick Celtic put Greenock Morton to the sword during a rampant 5-0 Scottish Cup fourth-round drubbing at Parkhead.

Even allowing for the Championship-level opposition, the Aussie was at his imperious best. Any lingering doubters about Mooy had better step aside.

Getting a player of his class and calibre for nothing is actually some bit of business when you think about it. The fans are now marvelling at a player who is proving himself to be nothing short of a class act; he is fast becoming a massive player for the team.

"Aaron's been outstanding for us," Postecoglou said post-Morton. "The World Cup was a positive experience for him, helped him with his fitness levels and he's been a really key contributor."

Celtic Way:

Nobody of a green-and-white persuasion could or would argue with that sentiment. Celtic were clinical and professional once again with Mooy at the heart of everything that was good about the performance. He should have bagged his first treble in Hoops colours but the width of the post denied him that honour.

"I thought it was really professional," Postecoglou added on the performance in general. "The lads stuck to our principles and worked really hard. Sometimes against players like this you fall into the trap of thinking you don't have to work hard but I thought we worked hard for the whole game, scored some good goals and, yeah, I'm pleased."

So Postecoglou should be. His intimate knowledge of the J1 League has served Celtic well in the market so far too. It's worth noting that in this match Kyogo Furuhashi took his goals tally to 20 for the season which matched his total for the whole of the last campaign... in January.

It was also Postecoglou's intimate knowledge of a player that he had worked with at international level that has done Celtic a turn again. Many sneered at the thought of recruiting Mooy, labelling him a spent force in the process. Those predictions are looking wildly inaccurate and foolish right now.

Postecoglou is, it must be said, also in danger of having solved the team's penalty kick issues in the process as Mooy has now slammed home two out of two since assuming the responsibility from 12 yards. Take out of that what you will.

READ MORE: Detailed Celtic player ratings as Celtic crush Morton in Scottish Cup

Postecoglou knew what he was doing all right when he brought Mooy into the Celtic fold. The Celtic manager doesn't just sign good footballers he brings good people to his football club.

As Postecoglou once said: "There is something to be said for that, just working hard for your family and being a decent person. I say it to the players all the time. You can have all the money and fame, but there is nothing wrong with just being a decent person.

"I always believe that environment and culture are driven by people and not me trying to enforce conditions on how the players should be. If you get the right people that kind of drives itself. I am really big on everyone in this building being respectful of one another and being good people - there is nothing wrong with that. In life we all grow up with intentions of being the best people we can be and that is what we strive for and I expect that here."

Compare and contrast that with what Mooy said when he was asked to sum up the win over Morton and his sterling contribution to the win.

"It is about the team, it is not about me," the 32-year-old said. "I am part of the team and when I play I try to help the team. It was a good performance from everyone and it was a nice way to end the week."

Selfless, humble, modest and all about the team, Mooy is as much as a class act as a footballer on the field as he is off it.

A good player and a good person? Two boxes ticked right there. They are exactly the two main reasons why Postecgolou brought him to Celtic in the first place.