It has been 11 years since Jose Mourinho's iconic sprint down the touchline as his Porto side eliminated Manchester United from the Champions League.
That night at Old Trafford announced the 'Special One' to the world and he would subsequently guide Porto to European glory that season. Now three clubs and 16 trophies later, he finds himself in the most difficult period of his career, as his second spell at Chelsea threatens to come to a familiar end.
Meanwhile at Manchester United, the club continues to rebuild following the departure of Sir Alex Ferguson.
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The Scotsman's retirement had a disastrous impact on the Red Devils and it has now been left to Louis van Gaal to lead the club back to the top.
The Dutchman delivered a satisfactory fourth-placed finish in his first season at the club, but the pressure is now on for him to deliver a trophy in his second season at the Theatre of Dreams. However, that goal looks more and more unachievable each time you see his side play.
This has been a period unlike any other for Mourinho. He has never experienced such a difficult spell, so perhaps understandably, he has not handled it well.
The problems continue to mount up for the fallen champions, who find themselves sitting 16th in the table, 15 points off the top and only four clear of the relegation zone. It's been a totally unexpected slump for a side that looked utterly unbeatable at times last season.
Their rock-solid defence has shipped 23 goals already, having only conceded 32 in the entirety of 2014/15. Star performers such as Nemanja Matic, Cesc Fabregas, Eden Hazard and Diego Costa have looked a shadow of their former selves while the man at the helm has hardly covered himself in glory either, it's been a season plagued by controversy so far.
The self-confessed 'Happy One' has looked anything but this season and has faced the high-profile Eva Carneiro incident and several FA charges. The 52-year-old looked a broken man as he refused to answer questions following Chelsea's 3-1 defeat to Liverpool.
DISCONTENT AT UNITED
The pressure on Van Gaal is by no means as great, but make no mistake it is there.
The 64-year-old has made a rod for his own back by spending nearly a quarter of a billion pounds on new recruits. There have already been high-profile failures in the shape of Angel di Maria and Radamel Falcao while Memphis Depay is in danger of joining that list if he doesn't improve.
Certainly United fans are entitled to expect more given the reputation of their manager and the money he has been provided. The 20-time champions just about scraped a top four spot last season and their start to the new campaign has not been wholly convincing.
Van Gaal's side are just two points off the summit but feelings of scepticism are at an all-time high amongst the Red Devils' fans.
Despite a more convincing victory over West Brom, the general feeling suggests results have - at times - flattered United and many continue to bemoan the tactics of Van Gaal. The dull, possession-focused football, which resulted in three consecutive bore draws has been openly criticised and even when United emerged victorious against CSKA Moscow there was still a feeling of unease.
The clearest indicator of fan discontent came in the 66th minute as boos greeted the substitution of Anthony Martial for Marouane Fellaini. It's simply not acceptable to be spending over £200 million and resorting to lumping the ball to the Belgian each time United are struggling.
While Chelsea fans have rallied behind Mourinho, United followers appear to be running out of patience with Van Gaal.
SACKED IN THE MORNING?
Mourinho's behaviour over the last few weeks has been inexcusable, but despite that, there can be no denying that he is still one of - if not the best - managers in world football.
It has been without doubt, the worst spell of his career, but the Portuguese boss is still good enough to manage any club in the world.
He should consider himself lucky to still be in a job, though, Roman Abramovich has never backed a manager like he's doing right now. The Russian will hope that his faith in Mourinho is repaid in the coming months.
The title is gone and Chelsea must accept that, now the focus has to be on sealing a place in the Champions League, meaning there must be a swift turnaround.
Quite where that turnaround is going to come from is another matter entirely, Mourinho is stuck with this group of players until January and the winter window is a difficult time to bring in new faces.
Mourinho may well be a fantastic manager and probably the best man to help turn the situation around, but there is still no guarantee he will be in charge come the end of the season.
It will, of course, depend on how patient Abramovich is, if there is not a marked improvement in the coming weeks then it wouldn't be a surprise to see the 52-year-old depart.
The Manchester United board will be reluctant to part company with another manager, but we must remember that fans have a massive influence on football clubs and van Gaal is starting to lose them.
The current group does not look to have enough quality to win the Premier League title and that will be a concern for everyone associated with United. How they can spend a quarter of a billion and look so inferior to Manchester City and Arsenal is beyond many.
VAN GAAL OUT, MOURINHO IN?
So what would constitute a successful season for United? Well, at the start, the talk was of a title triumph, but that seems like wishful thinking.
Is 'progress' really enough return for the investment that's been made? Third or fourth would simply not be good enough considering the resources at the manager's disposal. If van Gaal is not lifting that Premier League title come May then serious questions need to be asked about his future at the club ahead of the final year of his contract.
Van Gaal being sacked is certainly not beyond the realms of possibility as failing to deliver a trophy would be a disaster for the club. The question then would be, who next?
Ryan Giggs is seen as a future manager of the club, but only after the expiration of the Dutchman's contract in 2018. Would the Welshman be ready to step into his shoes a year early?
If Mourinho was out of work in the summer and United without a manager, then surely the board would be tempted.
Mourinho has been linked to the role before, of course, and allegedly 'cried' after being overlooked back in 2013. There can be little doubt that the former Real Madrid boss would have excited the fans more than David Moyes.
The Chelsea manager claimed to have his heart set on a return to the Blues, but that wouldn't be a problem if he's deemed surplus to requirements by Mr Abramovich. Surely United could not overlook him again.
A manager who has won trophies where ever he's been, including England, seems the perfect choice for a club of United's calibre.
Mourinho has the charisma and winning mentality that you would expect of a Manchester United manager, some would argue Van Gaal is lacking both.
They might be mocking him now, but one would imagine there would be few objections if Mourinho were in charge at the start of next season.
Mourinho announced himself to the world at Old Trafford, perhaps it could be where he repairs his damaged reputation.