It was the day that Chelsea fans had always feared from the moment their most successful ever manager in Jose Mourinho was ludicrously sacked back in September 2007.
The day that Mourinho would return to Stamford Bridge with a rival team and crush Chelsea's hopes when it mattered most.
Indeed Inter Milan's stunning 1-0 win in the second leg of their European Champions League clash with Chelsea on Wednesday morning to cap off a 3-1 aggregate win must have felt like a knife through the heart of every Blues fan worldwide.
There was the man who, for an all-too-brief period, had made Chelsea - for so long one of the great underachievers of English football - the king of England now engineering its downfall with the Italian giants and all because Chelsea owner Roman Abramovich incredibly decided he was dispensable two-and-a-half years ago.
Mourinho should have been Chelsea manager for life in much the same way that Sir Alex Ferguson has become a permanent fixture at Manchester United - having been in charge since 1986 and continued to deliver them trophy after trophy, year after year.
The other big gun of English football in Arsenal has enjoyed similar stability under Arsene Wenger, who has been in charge since 1996, but when Mourinho arrived at Chelsea and promptly delivered the club's first English title in 50 years in 2005, the Blues looked set to not only take over as England's No.1 club but also become the kings of Europe as well.
Mourinho would deliver another title the following season at Chelsea as well as two league cups and one FA Cup during his brief period in charge to become the most successful manager in Chelsea's history.
But his failure to deliver the European Champions League plus personality clashes with owner Abramovich led to his departure in September 2007 and Chelsea has not been the same force since.
Even at the time it appeared to be one of the worst decisions imaginable by a professional football club and with the benefit of hindsight over the years since, it only appears even more unfathomable.
Remember it took Ferguson 13 years to win the European Champions League for Manchester United while Arsenal is still yet to win the world's biggest club competition under Wenger.
Mourinho then joined Inter Milan at the start of the 2008/09 season and promptly won the title in his first season and now he has restored some much-needed pride to Italian football by knocking out his former club on its home turf.
But while Inter Milan's victory ensured the presence of at least one Italian club in the last eight of this year's European Champions League, Chelsea's season is in danger of disintegrating.
While new manager Carlo Ancelotti has done a far better job than his predecessor - the axed Luiz Felipe Scolari (with only the late presence of Dutch master Guus Hiddink rescuing Chelsea's 2008/09 season in winning the FA Cup, the club's only trophy since Mourinho's axing) - the Blues are now staring at going trophyless in 2009/10.
At a time when they are already under siege following the John Terry sex scandal, they have since conceded the lead in the EPL title race to Manchester United and now they are out of the Champions League having already been knocked out of the league cup earlier this season.
While the EPL title race is still very much alive - and Chelsea is still involved in the FA Cup - with just two points separating United, Chelsea and Arsenal at the top of the table, the Blues are running out of momentum while at the same time the Red Devils and the Gunners are surging.
It would be easy to blame the media circus that Terry has heaped on the club - following his affair with the ex-girlfriend of former team-mate Wayne Bridge - for the Blues' current problems.
In truth Chelsea's problems began the day it stupidly sacked Mourinho.
But someone's loss is always someone else's gain as Blues fans found out the hard way against Inter Milan.