The English Premier League (EPL) has never known a title decider like this, simply because it has never known a title challenge like this.
Leicester are the underdogs who have become top dogs. The ultimate outsiders are 180 minutes away from being anointed favourites to win the EPL.
The obstacles in their path are their next two opponents, Manchester City and Arsenal.
There was a time when City's reputation as lovable losers made them the neutrals' favourites. Now Leicester have become many people's second team, simply for their capacity to upset the odds and the established order.
The wealthier, more established City spent £158 million (S$321 million) last summer. They have the financial muscle to power to the title.
Leicester don't. Instead, they have an extraordinary momentum, a unity and a sense that this is a unique opportunity they can grasp.
They have the freshness - they are in one competition to their opponents' four - and the fitness, with no significant injuries, whereas Manuel Pellegrini is without Vincent Kompany and Kevin de Bruyne.
Leicester also have resilience. When the goals dried up at one end, they started keeping clean sheets. Now they have also scored five times in two games.
After a seven-match drought, Jamie Vardy has three in two, including a goal-of-the-season contender against Liverpool on Tuesday.
Sergio Aguero and Vardy symbolise the difference between contrasting challengers: The Argentinian has the pedigree and the class, the Englishman has raw hunger and an opportunistic streak that makes the spectacular possible.
City have the third-highest possession in the league, Leicester the third-lowest. They will happily use Vardy's counter-attacking pace and it could prove a successful ploy. While Pellegrini's men have four clean sheets in six league games, they remain susceptible defensively.
Each manager's principal selection dilemma comes in the centre of the pitch.
Does Claudio Ranieri abandon his 4-4-2, bench Shinji Okazaki, leave Vardy alone up front and bring in another central midfielder to patrol a territory where City are often at their slickest?
Does Pellegrini trust Yaya Toure as one of the two deeper players when, in an equivalent role, Leicester have the all-action ball-winner N'Golo Kante, or does he select him as a No. 10?
The probability is that both will be bold. Their convictions have taken them this far. While these two teams drew 0-0 in December, the fact that both retain an attacking ethos suggests a repeat is unlikely.
Ranieri's daring has made a historic feat possible. Pellegrini's adventurous streak could be the key to his future. When he departs and Pep Guardiola arrives, it could be as a double champion.
For now, the equation is simple. Win and Manchester City knock Leicester off their perch. Lose, however, and Ranieri's men would have a commanding lead. The impossible might seem probable.
MANCHESTER CITY V LEICESTER
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