"The fans were absolutely brilliant," said Sir Alex on MUTV. "When our crowd gets like that, we never let them down. They make such an impact, they force us to play."
The United players responded with some tremendous performances, and one in particular caught the manager's eye.
Arguably the only thing Tevez's performance lacked was a goal. The same has been said of Paul Scholes several times this season but he picked the perfect moment to end a barren spell dating back to last August.
"He scored in the second game of the season at Portsmouth and then today he's come up with another one!" remarked Sir Alex. "We've seen so many great goals from Paul in the past but tonight, considering the occasion and the importance of the game, he scored an absolutely magnificent goal."
The comfort of a second goal never came, so it was an anxious evening all round for fans, players and even the most seasoned of club staff.
"I just hope my pacemaker's working! If not, I'm in trouble!" quipped the boss.
"It was excruciating, that's what it was. The pain and the agony - I always feel that to get success, the players have to endure that. All the hard work, all the pain and torment you go through in football is rewarded by a result like tonight's."
Sir Alex's delight at the result was heightened by the calibre of United's opponents.
"Our home form in Europe has been absolutely outstanding and it needed to be tonight because I have to pay great credit to Barcelona, a club with great philosophy," he added.
"Their sportsmanship at the end of the game showed what a great club they are.
"I just feel tonight we have beaten a fantastic football club and a great team and that puts our performance in perspective. I think it was marvellous."