DJ and Paulina had an impromptu range sesh with their 2-year-old outside their home Tuesday ... and thank God someone brought the camera -- 'cause the Great One's grandson can seriously hack it.

Watch the clip ... River Johnson has the classic DJ backswing and he keeps his head down throughout the whole stroke. Plus, he even takes a little bit of a divot!!!

The swing clearly impressed Mom ... 'cause Paulina said of the vid, "Watch out pga tour 2035."

Even Grandma loved seeing it, with Janet Gretzky saying, "Takes after his Grandma Honey!!! Go get it River !!"

Of course, the athletic feat shouldn't surprise a soul ... Dustin's one of the greatest golfers of all-time and Paulina is the daughter of the best hockey player ever.

But, don't worry too much about the Gretzkys not carrying on the hockey tradition ... River's pretty good with a stick too -- remember when he put pucks past grandpa earlier this year?!?!