His next fight will be for a world championship.
Whitfield defeated Sergio Espinoza with a technical knockout in the ninth round in front of a vocal crowd at Bell Auditorium.
"It's another stepping stone to the top," Whitfield said after taking possession of the championship belt in the ring. "Our people will go back to the drawing board and see what we can work out."
Whitfield was in command from the start, landing a number of punches against his opponent.
The Augusta boxer known as "Stingray" put Espinoza on the mat in the second and seventh rounds, but he landed the deciding blow at the 2:49 mark of the ninth round.
With Espinoza backing toward the ropes, Whitfield landed a big right hook and the "San Diego Sensation" crumpled to the mat. He got back up, but then signaled that he couldn't go on.
The partisan crowd rose to give Whitfield a standing ovation, and he was soon joined by family and friends inside the ropes.
Whitfield's local trainer, Tom Moraetes, said before the fight that it was a must win for his boxer. The NABO title was vacant -- Whitfield previously held it -- and the winner automatically became No. 1 in the rankings.
"It couldn't get any better. A guy like that, hard to take out, everything came together," Moraetes said. "He won and he looked good."
The victory improved Whitfield's record to 24-1, while Espinoza's mark dropped to 16-7-1.
Weeks of preparation paid off for Whitfield, who said he had faster hands than his opponent.
"Everything he brought to the ring I knew he was going to bring," Whitfield said. "I was ready for it."
The main event capped a night of boxing with seven bouts on the card. Most of the fights were decided by knockout or technical knockout, and only two required decisions by the judges.
Even though the event wasn't sold out, the evening was judged a success by TKO Boxing Promotions president Chet Koerner.
"We've got a great crowd tonight, and everyone came out to support the local hometown hero, Rayonta Whitfield," Koerner said.