Adele ditched Las Vegas to hang with her boyfriend Rich Paul -- and she had a good reason ... it's the dude's birthday, which means the whole Klutch Sports crew tagged along.

The singer was rolling deep with LeBron James, Anthony Davis and other Klutch clients for the super agent's 42nd born-day party Saturday night ... which went down at a WeHo venue -- where everybody filed out of one exit towards the end of the night, it seems.

As you can see, RP's biggest claim to fame King James was front and center, leading the huge pack of people outside ... suited and booted with his wife, Savannah, close behind.

AD was with his own wife too, and ditto for Kevin Hart ... who was in the mix as well.

As for Adele and Rich, they were shoulder-to-shoulder as they left the joint ... and both looked dressed to impress, albeit not looking nearly as cheerful as you'd think while walking out.

Anyway, they're clearly still going strong ... this after a lengthy residency for Adele, who was in Sin City for a majority of this year -- and who's actually scheduled to head back in 2024.

You'll recall, she constantly referred to herself as Rich's "wife" out in the desert ... but it's unclear if they're actually hitched, or if it was just a slip of the tongue/term of endearment.