Ronnie Rivers almost matched his entire NFL rookie salary in one night ... 'cause the Los Angeles Rams running back won half a million playin' cards at a Vegas casino!!
The 24-year-old was at Caesars Palace in Sin City on Saturday when got lucky at the Mega Progressive Jackpot table ... and we're talkin' REAL lucky.
Rivers pulled a Royal Flush at the three-card poker table ... the most improbable hand you can hold. The odds of getting a RF are 1 in 649,000.
Rivers and his friends went crazy, and rightfully so .