*NSYNC's JC Chasez Attends Backstreet Boys Show in Las Vegas

Boy band worlds collided at the Sphere in Las Vegas ... because *NSYNC superstar JC Chasez hit up the venue to see the Backstreet Boys ... and he was treated like royalty.

Our sources tell us JC sat and watched the concert with James Dolan in his suite ... Dolan owns the Sphere, Madison Square Garden and the New York Knicks ... so you already know those are good seats!!!

Before the show, JC went to dinner with his girlfriend, Jenn, his manager, Eric Podwall and President of Entertainment for MGM Resorts Ryan Abboushi ... and at the Sphere, he posed for some photos with Nick Carter, AJ McLean, Kevin Richardson, Brian Littrell and Howie Dorough.

The BSB shows have been a huge success, and it looks like JC had a great time.

*NSYNC hasn't been able to work out a reunion show just yet ... and it will be interesting to see if JC's experience here gets the ball rolling on that front.