Justin Bieber Shoots Hoops on First Twitch Live Stream

Justin Bieber's first Twitch live stream is shaping up to be a slam dunk ... 'cause he showed off his basketball prowess during his debut on the popular platform.

The singer-songwriter fired up his account for the first time Wednesday ... and, it captured him enjoying a shootaround with some pals -- tossing the rock up toward the basket.

When they finished with that, Bieber took to playing some pool ... so, it looks like the dude's in a gaming mood while hanging with his buddies in what appears to be a large warehouse -- complete with a ramp for skating.

Bieber's usually playing some kinda sport with his pals. Remember, just last week the guy played both basketball and indoor soccer ...…