The two music stars -- who have history dating back to the 2000s, figuratively and literally -- showed up shoulder to shoulder Saturday night to watch the Garcia/Davis boxing match ... where they had ringside seats right next to each other.

People noticed them almost instantly, and the cameras started to roll ... as seeing the two of them out in public like this is a pretty rare sighting -- and certainly could have implications.

It's not like Ashanti or Nelly were trying to hide, but they did seem to be laying low a little bit. Of course, Twitter lost its s*** when another video of them leaving the main floor surfaced ... which shows them holding hands. Nelly, specifically, grabs a hold of Ashanti.

Later, they were spotted in the tunnel with their entourage and were pretty close to one another in this instance as well ... and even got asked some questions on camera.

After they both answer, the two of them appear to head off in the same direction ... again looking to be holding hands. It could just be friendly, with Nelly playing the gentleman and leading Ashanti out of a crowd by taking the lead. But, that's not how a lot of people see it.

Considering they used to be together back in the day -- something that just came to light not too long ago via stories shared by Irv Gotti, etc. -- folks are thinking they're a couple again.

They well may be ... time will tell, we suppose. If we see 'em out in public again, it could be the final nail in the coffin to confirm they're back on all these years later. Their last public reunion appeared to be nothing but a stunt/troll, but now ... this could be the real deal.