Manchester United's 1998/99 season is the stuff of legend.
It was the campaign which saw Sir Alex Ferguson's team become the first - and still only - English team to win the treble.
The Red Devils were just a different animal that season, showing a remorseless and never-say-die attitude in a number of big games.
But if one game was to define that 1998/99 season, it was United's trip to Juventus in the Champions League semi-final after a 1-1 draw at Old Trafford.
The Italian giants were virtually unbeatable on their home patch and were the overwhelming favourites to progress to the final at the Nou Camp.
The Irishman's performance that night in Turin was utterly ridiculous. Not only did he keep Juve's attack at bay, but he contributed heavily in attack.
His highlights package from the game still looks barely believable even 21 years on, that's how good Keane was that night.
Pipo Inzaghi's brace inside 10 minutes should have deflated United, but Keane grabbed the game by the scruff of the neck and made it a contest once again with a well-taken header from a free-kick on 24 minutes.
Goals from Dwight Yorke and Andy Cole in the second-half sealed the deal, but it was Keane who was at the heart of everything positive from United.
There is certainly a case for labelling his performance as the greatest midfield display of all time.
To do that in one of the biggest games in football is just staggering and it's testament to just how good of a player Keane was.
The Irishman was far, far more than just a midfield destroyer. His first touch was impeccable and his ability to be a threat offensively was key to how Ferguson's United operated.
Both Keane and his arch nemesis at the time, Arsenal legend Patrick Vieira, were once-in-a-generation midfielders and we haven't seen anyone quite like them since.
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