Douglas Lima says he ain't just the best welterweight in Bellator ... he's the best freakin' welterweight MMA fighter on planet Earth.
Yes ... ya listening Kamaru Usman? 'Cause Lima says (in the most respectful way ever) he knows for sure he'd beat you!!
TMZ Sports talked to the 31 year old Lima -- who's got a record of 32-7 with wins over beasts like Michael "Venom" Page and Paul Daley -- 2 days after his Bellator Grand Prix title win over Rory McDonald.
The prize?