On that day, with Porto leading 2-1 from the first leg, and United trailing the Premiership leaders - and eventual champions - Arsenal by eight points, Mourinho arrived to inflict a shattering blow on Ferguson's season. The similarities between then and now could hardly be more foreboding for United: they are 13 points behind Chelsea in the Premiership and, like the match with Porto, they have to beat one of the emergent teams of Europe - Villarreal - to stay on course in the Champions' League. The major difference is that this crisis is taking place four months earlier in their campaign than it did two seasons ago.
Ferguson and Mourinho: they have not always been on such good terms. It is doubtful whether the United manager expected to enjoy a long and meaningful friendship with his opposite number as Mourinho disappeared into the pile of Porto players celebrating a decisive last-minute Costinha goal at Old Trafford. There will, no doubt, be a good deal of mateyness and jocularity about the post-match wine's quality, but the impact of a Chelsea victory this weekend would have a significance for the future of United and Ferguson that neither man will underestimate.
Both managers are understood to have convened meetings of their players this week to make the point that tomorrow's match represents a crucial stage of the season. For Mourinho that has meant little more than a frank admission to his players that he feels there has been a sloppiness about their approach to their last four games, of which they have won one.
For Ferguson it has been much more serious: he has been forced to confront the issue of Roy Keane's infamous MUTV interview and yesterday he echoed the sentiments of Mikaël Silvestre that beating Chelsea is the last chance his team have to salvage their domestic season.
It is very rare that Ferguson goes into a match as important as tomorrow's game with so few options to change his team. No Ryan Giggs, Roy Keane, Gabriel Heinze, Gary Neville, Louis Saha or Quinton Fortune leaves him with few chances to adapt his midfield or attack if his starting XI start poorly. It seems inevitable that Alan Smith will continue his re-education as a defensive midfielder against the best in the business, Claude Makelele, and that Paul Scholes will occupy the space alongside him. While Cristiano Ronaldo will start, Ferguson has a choice between Darren Fletcher and Park Ji-Sung for the last place in the midfield.
Against a manager whose strategy is to plan for every eventuality a football match may throw up, United are hardly in a position to baffle Mourinho with endless tactical variations. They also have their two first-choice full-backs out injured which will mean that Silvestre, and either John O'Shea or Phil Bardsley will be under intense pressure to cope with the two wide players that Mourinho picks from up to four wingers.
Another fascinating aspect will be Chelsea's approach to handling Wayne Rooney, who has not scored in his last four games, and must now sparkle againstJohn Terry, the best defender in the Premiership. Rooney's normal reaction to the frustration of being denied possession and space is to come deeper into the opposition territory which will align him with Makelele and Michael Essien - as formidable a pair of spoilers and tacklers as he is likely to meet.
There is the added dimension of how the two sides' benches compare and, with the attacking options that Mourinho boasts, it is there that Ferguson will feel the pinch the most. It is odd that the stakes have not been pushed any further by Ferguson than his complaint yesterday that Chelsea have changed the business of transfers - hardly the kind of provocation he has employed in the past.
Back in March 2004, when Mourinho, the relatively unknown Porto manager, laid down a supremely confident challenge to Ferguson, he showed his mastery of a phrase that had recently become a crucial addition to the English football vernacular. "You say 'mind games'?" he asked at the time. "Yeah, they are no problem to me." And with that he launched into an attack of Ferguson's claims that his players had dived, suggesting, along the way, that a club with such history and reputation, not to mention 65,000 fans behind them, were unaccountably showing signs of fear.
Since then, Ferguson has employed none of the "mind games" on Mourinho that he has used with varying success against Kevin Keegan and Arsène Wenger. There was one half-hearted attempt to suggest that Chelsea might have a problem playing away in the north last season, but Mourinho's side made such short work of that hypothesis that the United manager has not advanced another since. Instead there remains this strained bonhomie among the two men and Mourinho's studied reverence of Ferguson while, in the meantime, his Chelsea team undermine much that the United manager has built.
It is an odd relationship, and one that seems at odds with what we know of the characters of these two men. Mourinho will covet Ferguson's unassailable place in history and Ferguson no doubt appreciates the younger man's achievements - his raffish approach and the linguistic skill that skips effortlessly between three different languages in one press conference. But when there is so much at stake what, it seems, Ferguson really needs to fire his players' imagination is the Mourinho who first visited Old Trafford: a clearly defined enemy.
* March 1996 Premiership Newcastle 0 Man United 1
Newcastle had enjoyed a 14-point lead in the League but United had cut it to six.United won seven of their last nine games - and the Premiership.
* April 1999 European Cup semi-final, second leg Juventus 2 Man United 3
(United won 4-3 on agg)
Goals from Roy Keane, Dwight Yorke and Andy Cole brought United back from 0-2.
* April 2004 FA Cup semi-final Arsenal 0 Man United 1
Paul Scholes scored the only goal of the game that ended Arsenal's attempt to win the treble.
* Oct 2004 Premiership Man United 2 Arsenal 0
Goals from Ruud van Nistelrooy and Wayne Rooney ended Arsenal's 49-game unbeaten League run, sparking the "Battle of the Buffet".Reuse content