Chris Brown and Usher Spark Feud Rumors After Disastrous Atlanta Concert

Chris Brown and Usher had fans waiting hours to see them perform ... only to leave concertgoers wondering what the hell they'd just paid for.

The R&B stars kicked off their five-night run at Atlanta's Mercedes-Benz Stadium Thursday ... but fans say the show didn't start until around 10 PM, roughly two-and-a-half hours late.

And the late start was just the beginning ... concertgoers complained the pair didn't perform a single song together, with large chunks of the setlist apparently getting the ax.

One disappointed fan called the show "very underwhelming" ... others demanded a refund from Ticketmaster ... and many blasted the performances as rushed, with some declaring they'd never attend another concert by either singer.

The backlash quickly sparked speculation that Chris and Usher were beefing behind the scenes ... with fans suggesting a feud could explain the missing duets and shortened performances.

Chris appeared to shut down the rumors, posting a message to his Instagram Story reading ... "Internet 🧢. don't fall for it."

He didn't specify what he was referring to, but the timing certainly raises eyebrows.

The rocky start comes as the two are making history in Atlanta ... becoming the first artists to perform five shows at Mercedes-Benz Stadium during a single tour stop, breaking Beyoncé's previous record of four.