Athletic Club had beaten Ferguson's English champions and the United manager was facing the media deep in the bowels of the old stadium last modernised 30 years ago. A huge photo of a victorious Athletic team sailing up the River Nervion through the city, surrounded by an armada of boats and thousands of delirious people on the river bank, dominated the room.
Ferguson was full of praise for the Basques.
"I wish them well," he said. "They have a cause. It's a wonderful thing to see, using such incredible energy to win football matches."
"Their work rate higher is than anyone I've seen in Europe. They showed some very good combination football and could have scored two or three in the spell after half-time. There's a very good chance they can win it."
Mad genius Bielsa in Old Trafford press conferenceAthletic's Argentinian coach Marcelo Bielsa was soon in the same seat. Although victorious, he didn't have the same enthusiasm, nor force of personality. Bielsa looked unkempt, downtrodden and had awkward mannerisms. He stared at the floor and his answers, delivered very slowly, bordered on boring when he can in fact be fascinating. He seemed a reluctant interviewee. Bielsa had just seen his team overcome United as they aim to reach a first European final since the 1977 UEFA Cup final, which they lost on away goals to the Juventus of Dino Zoff, Claudio Gentile, Marco Tardelli, Roberto Bettiga and Gaetano Scirea - and managed by Giovanni Trapattoni.
The past means nothing to Bielsa and he was reluctant to make comparisons. He's no Mourinho with the media — and he has no desire to be.
One former Manchester United legend sat next to me in the press conference and whispered to ask if Bielsa was okay mentally. I explained that two words which normally prefix the word Bielsa are 'mad' and 'crazy'.
It is substance, not style, that matters for Bielsa, a man Pep Guardiola describes as "the best coach on the planet". He is a genius who doesn't bow to convention and doesn't care. Sometimes he doesn't speak to his players, sometimes he speaks to them non-stop. He does everything his way.
Under his leadership this season, Athletic have improved. He inherited a very good squad from Joaquin Caparros, one which reached the 2009 Copa del Rey final and has finished in successively higher positions for the last three years up to last season's sixth. Athletic had been in danger of a first ever relegation in 2007 and their Basque-only policy was seen as anachronistic by some - but Caparros nurtured and guided an emerging group of players.
Caparros was dismissed by a new 43-year-old club president who wanted Athletic to play, well, a bit less like Athletic. The Lions have a reputation for playing like an English side; fast, physical and direct. It wasn't always pretty.
Bielsa was charged with bringing beautiful football, but he didn't start well. Athletic were 18th and winless after five games before the cream of Iker Muniain, Fernando Llorente and Javi Martinez began to rise. In November, they were on the cusp of beating Barca in arguably the best game seen in Spain all season until Messi grabbed a last-minute equaliser.
Athletic excelled in the cups too. They have won seven and drawn one of their Copa del Rey ties this season, enough to get then to a final in Madrid against Barcelona. In the Europa League, they've won seven, drawn one and lost two, the two victories over United the highlight of their recent history. And unlike 14 of the 20 Liga clubs, they've not done it by going into debt and falling behind on tax payments.
I was in Bilbao last week and I've never seen anything like it. A one-club city, the whole place was buzzing in anticipation for the game, with people of all ages wearing red and white and thousands of flags adorning Spain's fifth-biggest city.
The 1,000 travelling United fans couldn't believe what they were seeing, either. They're often met with hostility on their travels, but in Bilbao they weren't allowed to buy their own beer.
Inside the stadium, the atmosphere was more Istanbul than Iberia and visitors like Ryan Giggs were given a standing ovation, as was Wayne Rooney's goal. It's easy to be magnanimous in victory - but still.
Athletic's players celebrate eliminating Manchester UnitedAfter the match, the away fans were applauded and welcomed into a party where tens of thousands of fans filled whole blocks of the city. And all because their football team won a game or two.
United fans were asking if it was always like this. After a big win it is. Athletic usually fill their stadium and that's why they're building a bigger one next door, which will open in 2014. As well as sating demand and replacing the atmospheric but ageing Sam Mames, it will give Athletic more financial muscle from extra seats and executive facilities. Their top players who are coveted elsewhere might feel less inclination to move for economic reasons.
Athletic are on the brink of (relative) greatness and the feel-good factor around the club is astonishing. So many neutrals admire what they stand for and wish them well, yet their greatest enemy is themselves. Athletic have played 19 cup games so far this season, more than any other team bar a Barca side with a far better squad. Seven Athletic players have started 40 or more games this season. Not one Madrid player has done that, nor a player from Valencia, while only Lionel Messi has started more than 40 games for Barca. Athletic have every right to be knackered and they looked flat as Valencia won 3-0 on Sunday on the same pitch on which United had been outclassed 72 hours earlier.
They'll hardly get chance to stop and breathe, not now or post-season, when several of the players will expect to be in Spain's Euro 2012 squad. Athletic have supplied more players to the Spanish national squad than any other team, Barca and Madrid included.
The Basques play Atletico Madrid tonight in a league game - they're currently ninth - but, like most of the league which is the tightest in Europe after the big two, they're still in contention for a European place. Next up in Europe are Schalke. If Athletic win one of the cups in which they've thrilled so many, expect scenes similar to the photo in the room where Ferguson and Bielsa spoke.
For that was taken in 1984, when Athletic last won a trophy - the league. And the cup. And the Super Cup. Just one trophy would suffice this time and even if it isn't to be, this side will be remembered with deep affection.