Kendall Jenner Packin' On PDA With Devin Booker ... At U.S. Open

There was a ton of action on the court at the U.S. Open men's final on Sunday ... but there was even more in the stands, 'cause Kendall Jenner couldn't keep her hands -- or lips -- off her NBA star boyfriend, Devin Booker!!

The couple has been inseparable recently -- they hit up the NBA 2K23 launch party in Los Angeles on Thursday, before jetting off to New York City for the weekend.

Jenner and Booker hit up a bunch of New York Fashion Week events throughout the weekend ... sitting front row in multiple flashy outfits.

Amid all the fashion week fun, KJ and DB showed up in Flushing Meadows as Carlos Alcaraz took on Casper Ruud ... and throughout the match, you can see they were passionately…