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Jay-Z will have an extra close eye on the NBA Finals this year ... 'cause the hip-hop mogul just placed a gigantic wager on the Oklahoma City Thunder winning the 'chip in five games!

TMZ Sports has learned Hov threw down $1 MILLION with good friend Michael Rubin 's Fanatics Sportsbook ... and if he's right, he will profit $2,300,000, on top of the milli he wagered (he'll walk away with $3.3m total).

The Thunder, led by this year's NBA MVP, Shai Gilgeous-Alexander , are heavy favorites to beat Tyrese Haliburton 's Indiana Pacers. Getty

But, Jay's bet isn't as simple as picking the overwhelming fav to win ... it's gotta be in five games, meaning the Thunder cannot lose more than once in the best-of-seven series.

It's a bit of a longshot ... though if Jay-Z

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