DeAndre Jordan -- Blasted with Water Cannon ... With Billy Crystal?!

Here's video that should make Mark Cuban happy -- DeAndre Jordan getting shot with a water cannon ... right in front of Billy Crystal.

Turns out, DJ -- along with Chris Paul and Billy (a huge Clips fan) -- were out in San Pedro, CA to shoot a commercial for the upcoming NBA season ... and it all went down on a boat.

Sources tell us the spot is supposed to show how the Clippers believe they'll "weather the storm" of the off-season (including the DeAndre contract mess) ... and dominate during the '15-'16 run.

At one point, you can hear Crystal say, "Hey DJ, is the whole season gonna be this rough?"

We'll see ...