A THIRTY-SIX-point swing would probably clarify the impact that Martin O’Neill had on Celtic. Tomorrow will mark the 20th anniversary of O’Neill assuming control of the club following the disastrous but brief “Dream Team” chapter of John Barnes and Kenny Dalglish.

The ignominious Scottish Cup defeat to Inverness Caledonian Thistle ended Barnes’ career at Celtic – but if that remains an embarrassing nadir, time has come to frame it as pivotal in revolutionizing the Parkhead side.

O’Neill’s arrival in June, 2000 saw a rebirth of Celtic as a substantial power shift took place within the city. Rangers’ domestic dominance was ended with the Irishman’s arrival; from losing the previous title by 21 points, Celtic went on to the win the league in O’Neill’s first season by 15 points as well as winning a Treble for the first time in 32 years.

Former Scotland internationalist Jackie McNamara featured in both eras. If he had to be patient at times as O’Neill favoured a 3-5-2 system with power and physique at the back, he still had a telling say in how that opening campaign ended.

The Scottish Cup win over Hibs which delivered Celtic’s first domestic treble since 1969 was kicked off with McNamara opening the scoring; Lubomir Moravcik had stitches in a leg wound from the previous week and had to be replaced early on with McNamara coming off the bench to net one and set up one in a comprehensive 3-0 win that emphatically confirmed O’Neill’s arrival on the Scottish football scene.

“It was an amazing feeling but the turnaround was just incredible,” recalled McNamara. “It is so difficult to explain why. Martin just had a real aura about him.”

The Celtic support were charmed by the charismatic O’Neill. By turns self-effacing, witty, sarcastic, caustic and entertaining, O’Neill went on to deliver as many titles and European wins in his five-year spell as Celtic had enjoyed for the previous 18 years.

But while there was an affable side to O’Neill, it wasn’t one readily seen by the players. If that infamous defeat to Inverness was notable, it also revealed the issues within the Parkhead dressing room. From Mark Viduka binning his boots at half-time and refusing to play again and Ian Wright chuckling at the nonsense of it all, there was a revelation of just how fractured and lacking in leadership Celtic were. It did not go unnoticed by O’Neill.

“Martin didn’t suffer fools gladly and he let people know if they had stepped out of line,” said McNamara. “It really was a case of my way or the highway – and that was there from his earliest days at the club. I remember one day at training when we hadn’t long got into pre-season when Stephan Mahe had a bit of a tantrum. Stephane was a lovely guy but he was known to lose it on occasion. Someone had kicked him in training and after throwing the toys out of the pram, he just turned and walked off the pitch. Martin didn’t bat an eyelid.

“He just shouted on him to keep on walking and he’d just been fined two weeks’ wages. He was back within a shot and, as you can imagine, fairly sheepish about it. But Martin definitely had an aura about him. You got a feel of it right away. Other managers sometimes let players away with this or that if they are big players or important players in the dressing room. There was none of that. He was about winning. He didn’t care about any of the nonsense because he wanted to win games. He had great guys there too in John Robertson and Steve Walford who were so important. They were the real link between the manager and the dressing room. But the change in psychology felt immediate. Everything was geared to winning. Everyone knew where they stood. He was straight and he was clever. He was brilliant in the dressing room right before a game.

“He obviously brought some really good players in to but he just had that man-management where players wanted to play for him. No-one wanted to be seen as the teacher’s pet and so there was this real collective in the dressing room.”

O’Neill took a broken Celtic side who had enjoyed only sporadic bursts of success – the 1995 Scottish Cup and the 1998 title win – and revised the mentality entirely. He won three titles, three Scottish Cups and one League Cup. He took Celtic took the UEFA Cup final, into the Champions League group stage for the first time, and kept them in Europe beyond Christmas for the first time in 23 years.

He did more than just restore broken pride. He raised the bar with quality signings from south of the border – the likes of Neil Lennon, Chris Sutton, Alan Thompson and John Hartson would be out of Celtic’s financial reach now – but there was an alchemy to the squad that went deeper than its personnel.

“There was quality in the team,” said McNamara. “But there was more than that. There was a chemistry and a real belief within the squad. The turnaround that first season was remarkable.

“There were some big characters in the squad, too. But there was just something about Martin that could get the best out of people.”

Signed from Dunfermline in 1995, McNamara’s first taste of silverware at Celtic was arguably the most important.

Part of the Celtic side which stopped Rangers winning a 10th successive trophy in 1998, McNamara can appreciate pressure and intensity of the season to come will be different from anything that the current crop of Ibrox players will have experienced before as his former team-mate Lennon looks to deliver an historic title this term.

“We had bought a few players and we had some big characters like Craig Burley and Paul Lambert [during the 1997/98 season]. But what I thought was crucial for us that season was winning the League Cup in November. It was a real shot in the arm.

“We had kicked the month off with a defeat to Rangers at Ibrox and I always remember Richard Gough going off the pitch and goading us.

“He was doing the big 10 fingers thing as the game finished and you are just thinking to yourself that it is a catastrophe to be a Celtic player if they go on and win the 10 league titles.

“Then, if memory serves correctly, we drew with Rangers and then that League Cup final was at Ibrox and we beat Dundee United. It just gave us such a lift. The pressure around that season was phenomenal. Going right into that last day it was really tough mentally because we all knew what was at stake.

“It is really difficult when you are on the opposite end of it and watching your rivals win everything.”

McNamara expects that his former team-mate can go one step further become the first Scottish club to win 10.

“I actually think Lenny had Celtic playing really positive, attacking football this season,” he said. “He really went for it after the winter break in terms of going all-put attack with the old 3-5-2 system back in place and it is great to watch. What was impressive was the lack of panic after the New Year defeat to Rangers.

“There were big celebrations but Celtic went away and kept their head down and just kicked on again. The players respond to him and you can feel the confidence in them.

I think it will take an awful

lot to stop them.”