Keldon Johnson is expected to be a 1st round pick in the 2019 NBA Draft -- and he's already rollin' around Hollywood like a BALLER!!!!

The former University of Kentucky star hit up Catch in L.A. for dinner and EVERYONE noticed when he pulled up ... behind the wheel of what appears to be a McLaren 720S Spider, which usually carry a $300,000 price tag!!!

You gotta watch the video with the SOUND ON -- the engine purrs like a tiger ... it's incredible. 

We asked Johnson if he's rooting for any particular team to draft him in June -- and he gave the answer any smart future NBA star would give!!