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UFC star Rose Namajunas has a message for Joanna Jedrzejczyk -- want a rematch? Hope you're ready to PUBLICLY stuff your face with a fat ol' piece of humble pie!

Of course, Rose already smashed Joanna TWICE -- ending Jedrzejczyk's historic 14-fight win streak. But Joanna wants a 3rd crack at the 25-year-old champ.

"She knows I'm the best," Rose tells TMZ Sports ... "But she won't admit it to anybody."

Well, if Joanna wants a third fight, Rose says that's gotta change.

"If she says that I'm the best PUBLICLY," Rose says ... she'll CONSIDER another rematch.

"Just say it!"

If JJ can't bring herself to make the public declaration, Rose says she's moving on with her life and career ... but doesn't rule out a 3rd clash with Joanna somewhere down the line.

"I'd be interested to see how she does with somebody else before even entertaining that possibility."