Joe Biden's Bracket Busted On Day 1 Of NCAA Tourney, Princeton Beats Arizona

Welp, Joe Biden isn't winning the White House's March Madness pool ... 'cause the president's pick for NCAA champion -- two-seed University of Arizona -- just lost to 15-seed Princeton in the most shocking upset of the young tourney!

The Ivy League team was near 15-point underdogs against Arizona ... but as the saying goes, that's why you play the game. The Tigers ultimately won 59-55. The Wildcats were up one at the half, but scored a paltry 24 points in the second half, and couldn't buy a bucket late in the game.

As for #46, he didn't just have AZ advancing past Princeton, he had the Pac-12 team going all the way to the Final Four, where he picked them to defeat one-seed Kansas.

In fairness to the prez, the Wildcats were a popular pick to advance far in the tourney ... and many had them winning the whole thing.

The Wildcats, who won the NCAA Championship in 1997, are now headed back to Tucson. The Tigers will now play seven-seed Missouri on Saturday ... where Princeton has opened as six-point underdogs.