The boy band basketball turf war just got REAL -- with Brian Littrell telling Joey Fatone that Backstreet will straight DOMINATE 'NSYNC on the hardwood.
And get this -- Brian says it'll only take 2 of the Boys to hoop up 'NSYNC's entire roster!
"They’ll lose, plain and simple," Littrell told TMZ Sports at LAX. "You can take myself and Nick against all 5 of those dudes and we’ll be cool."
Brian ain't playing -- telling us he's got a court at home to keep his game tight.
So, if Joey, JT and co. really want it like Fatone said, Littrell's down ... and says he wants 10 racks on it!!
"When we win, I’ll donate my $10,000 that I have on the game to charity. Joey can pick it."
GAME ON.