It was the moment when appeared to have the football world on the end of his twinkling Irish toes. The date was March 8th 2005 and mighty Barcelona were at Stamford Bridge for a Champions League showdown that exuded all the raw emotion you might associate with a heavyweight title fight in Las Vegas.
Blows were exchanged in equal measure until Duff burst clear of the Barca defence and fired home a goal that paved the way for Chelsea's assent to the top table of European football. Duff's glorious effort, complimented by skipper John Terry's dramatic late winner, positioned this likeable south Dubliner among the most prized assets in the game and yet his rise to mega stardom was never to materialise.
Injury problems and a dip in form meant he was not a regular for Chelsea in the season that followed and by the time he left the club in the summer of 2006, Duff found himself at a crossroads in his career and ultimately took a turn in the wrong direction.
Even though Tottenham offered him the chance to extend his stay in London, he opted to make a move to the North East oasis that has a habit of turning promising careers into stories of what might have been. Duff was not alone in becoming a victim of the curse that has been hovering over Newcastle United for all too long.
When he had the misfortune to score the own goal that signalled the end of Newcastle's Premier League existence last May, he could not have imagined that the lowest point in his career would become the catalyst for a personal revival in the capital city he grew to love during his time at Chelsea.
His move to Fulham last month appears to have been the ideal tonic to awaken Duff from his slumber and this 30-year-old admits the difficulties he suffered at Newcastle already seem like a distant memory as he prepares for Saturday's live ESPN game against Arsenal.
"It feels great to be back in a part of London that was good to me the first time around," begins Duff, whose initial stay in the capital saw him pick up two Premier League titles in Chelsea colours. "It just didn't work out for me at Newcastle and what has happened up there is a real shame. The North East is an area that lives for football and the fans are desperate for a bit of success, but it didn't work out for any of us and the off field problems didn't help the situation.
"In the end, it was best for all parties that I moved on and I was delighted to have a chance to work with a manager who I got on so well with at Blackburn in Roy Hodgson. Fulham has a lot of stability around it and that wasn't the same story for the club I left a few weeks back."
Duff was said to be Chelsea owner Roman Abramovich's favourite player in the days when he was the club's tormentor in chief, yet his fall from grace at Stamford Bridge was almost as rapid as his rise. After helping the club win their first domestic title in 50 years back in 2005, Duff started just ten games in the season that followed and was soon considered to be surplus to requirements.
"I loved everything about Chelsea and always said I never wanted to play anywhere else, but it was clear that I wasn't in the plans and had to move on," he reflects. "It was a shame because I was happy living in the south of England, my family loved coming over as it's easy to get to London from Dublin and it was a great time in my career.
"That's why I jumped at the chance to return to this part of the world when Fulham came in for me. I wasn't enjoying my football at Newcastle and needed a change, so I'm feeling very good about this opportunity."
Fulham boss Hodgson has used the seven days prior to Saturday's derby showdown with Arsenal to rest his star men, with Duff among those given some time off as he was excused duties for the Carling Cup tie against Manchester City. With their Europa League fixtures certain to stretch Fulham's resources to the full, Duff believes they can find a balance between domestic and continental ambitions this season. "Some people have said the European games are going to be a native for us this season, but I don't see it like that at all," he continues.
"Everyone at Fulham deserves credit for finishing seventh last season and getting into the Europa League. Doing well in that competition would give everyone a lift and we are certainly not looking at the games and thinking they are going to make life difficult for us."
Duff's return to the European stage at club level could well be a prelude to a second appearance at a World Cup finals next summer, with his Republic of Ireland side all but assured of a play-off place after enjoying a dramatic return to form under the management of veteran Italian Giovanni Trapattoni.
"Ireland's revival can be put down to our coach because he is top notch," believes Duff. "Trapattoni has worked with some of the biggest names in world football down the years and he has come into an Ireland team that was not doing too well and got us organised and winning games very quickly.
"We are grinding out results and that isn't something Ireland have been too good at in recent years. Our qualifying hopes were over a long time before the end in our last campaign, but we are in there with a chance of going to South Africa this time and it would be a great boost to everyone back home if we make it."
In an era when multi-millionaire footballers get too big for the boots long before they celebrate their 21st birthdays, this self-effacing star is a flashback to an era when the sport put talent ahead of celebrity.
Duff has always been something of a reluctant hero, but he looks ready to emerge from his extended period of hibernation and Fulham are set to reap the benefits.