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Nick Diaz is FIRED UP -- telling TMZ Sports he's still the BEST FIGHTER in his weight class ... and he's down to fight Tyron Woodley ... or ANYONE the UFC throws at him, if the price is right.

Woodley called Diaz out after he beat Robbie Lawler at UFC 201 this weekend -- and now that Diaz finished his suspension and can fight again ... Nick says he's ready to take on the world.

"I want to fight the best guy. I always want to fight the best guy. The thing is I'm on top ... I'm the one on top ... they're dropping MY name."

"I don’t need no fake ass piece of plastic. F*** that! I made PPV without a title. I don't need that fake ass plastic to be somebody."

For what it's worth, we're told the UFC is gunning to get Diaz a fight quickly -- but we're told the name being thrown around is Robbie Lawler.