Justin Bieber earned the J in his first name on Thursday ... showing off his solid jumper as he drained buckets in a basketball game.
The pop superstar showed up at The Surgeon's studio in Los Angeles to ball out in the famous shoe customizer's organized hoops league ... suiting up for Team Nahmias in their matchup against SRGN.
JB had a couple highlights in the contest ... showing off his range and passing abilities as he played alongside his longtime buddy Ryan Good and fashion designer Doni Nahmias.
It wasn't enough to help his team get the win, though .