Unofficial Champions of England: Southampton 3-1 Manchester United, 13/04/1996

Le Tissier scores for Southampton in the first half...

This game is somewhat infamous.

Manchester United were chasing the Premier League title and were now leading the table, having at one point trailed 12 points behind Newcastle United.

They visited The Dell unbeaten in 18 games in all competitions (including three as Unofficial Champions), winning 15 of them. They were blown away by Southampton in a first half blitz that saw The Saints lead 3-0 at half-time with goals from Ken Monkou, Neil Shipperley and Matt Le Tissier.
United did get one back in the second half through Ryan Giggs but too little, too late.

...something different about United in the second half

But its not the shock result that makes this memorable. What people remember is that in the first half, United were playing in their grey away strip, come the second half however they had changed to a blue and white number. The reason given was United players claimed 'they couldn't see each other' against the fans.
As excuses go, its pretty feeble. Needless to say, United never wore the grey strip again.

But some credit to Southampton, who took their second Unofficial Championship.