The event, from the Georgia International Convention Center, was King of the Cage's first in Atlanta.
Assuncao won a unanimous decision over Kamrin Naville out of Praxis/Valdosta MACA.
Assuncao improved his record to 7-4, while Naville fell to 4-4. Assuncao told MMAFighting.com earlier this week that his plan is to return to the UFC or join his brother Raphael in the WEC after this fight.
Also on the card, "The Ultimate Fighter 7" contestant Cale Yarbrough won by second-round knockout over Justin Hall and Charles Blanchard of the American Top Team won a decision over Douglas Lima.