May 26, 1999, was a night which simultaneously defied belief and defined Ferguson's Manchester United reign.
United were chasing history. The league title had been wrapped up, beating Arsene Wenger's Arsenal to the Premier League title by just one point.
FA Cup success followed. Goals from striker Teddy Sheringham and midfielder Paul Scholes secured a straight-forward 2-0 win over Newcastle United in the final at Wembley.
Ferguson's team were one step away from securing an unprecedented Premier League, FA Cup and European Champions League treble.
United's opponents in the European Cup final at Barcelona's Nou Camp stadium were Bayern Munich and the Germans looked set to win the showpiece match after Mario Basler's first-half free-kick put them 1-0 ahead.
In search of a way back into the match, Ferguson threw on substitutes Teddy Sheringham and Ole Gunnar Solskjaer.
As the game ticked into extra-time, United earned a corner. Goalkeeper Peter Schmeichel raced forward in a desperate attempt to force an equalizer.
The initial cross was cleared, but the ball fell to Ryan Giggs whose low shot from the edge of the box was turned into the net by Sheringham.
Cue jubilant celebrations among United players, fans and coaching staff, but uncontained joy was to follow seconds later.
United earned another corner kick in the final seconds of injury time. Sheringham flicked on Beckham's cross at the near post and Solskjaer flung his right leg at the header to send the ball flying into the back of the net.
Bayern were beaten, United had completed an historic treble.
As Ferguson remarked to ITV after the incredible climax, "football, bloody hell."