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.