Diogo Reis to defend ONE flyweight grappling title vs Carlos Oliveira at Fight Night 50

ONE Championship announced on Tuesday, November 3, that Diogo "Baby Shark" Reis will defend the ONE flyweight submission grappling world title against fellow Brazilian Carlos "Bebeto" Oliveira at ONE Fight Night 50 on Friday, December 18, at Lumpinee Stadium in Bangkok. The promotion posted the matchup on its official X account; MiddleEasy reported the same booking hours later.

The contest is a submission-grappling title match under ONE rules, not an MMA bout, and Oliveira is not UFC lightweight Charles Oliveira. ONE listed the show for U.S. primetime coverage, with Lumpinee as the venue. At the time of writing, the promotion's Fight Night 50 event page still highlighted Kade Ruotolo vs Ok Rae Yoon, Maurice Abevi vs Dzhabir Dzhabrailov, and two Muay Thai pairings, without yet listing Reis vs Oliveira on the graphic.

How Reis won the belt

Reis, a 24-year-old from Manaus who trains with Melqui Galvao, claimed the vacant flyweight submission grappling title at ONE Fight Night 38 on December 5, 2025, by unanimous decision over Daiki Yonekura. ONE's report described a 10-minute bout in which Reis repeatedly passed to side control, threatened an arm-triangle, and traded late leg attacks and a guillotine before the judges scored it for his aggression and submission offense.

He then moved up to bantamweight and beat Yuki Takahashi by unanimous decision at ONE Fight Night 43 on May 15, again after a full 10 minutes of back-control and submission attempts that Takahashi survived. Per his ONE athlete page, Reis is 3-0 under the ONE banner: a submission of Shoya Ishiguro plus the two unanimous decisions. ONE also named him Submission Grappler of the Year for 2025. Outside ONE, Reis is a two-time ADCC world champion at 66 kilograms (2022 and 2024).

Oliveira's challenge

ONE introduced Oliveira as a multiple-time IBJJF world champion making his promotional debut. The all-Brazilian pairing gives the newcomer an immediate title shot against one of the most decorated lightweights in modern grappling. Under ONE submission-grappling rules, championship matches are a single 10-minute round; if there is no tap, judges prioritize legitimate submission attempts ("catches"), with aggression as a tiebreaker and yellow cards able to erase a catch.

Fight Night 50 context

ONE Fight Night 50 is billed as the promotion's final U.S. primetime card of 2026. The MMA side already includes unbeaten grappling-to-MMA crossover Kade Ruotolo against former lightweight champion Ok Rae Yoon, plus welterweight Maurice Abevi vs Dzhabir Dzhabrailov. Adding a flyweight grappling title defense deepens a card that also carries Muay Thai matchups Suablack Tor Pran49 vs Jordan Estupinan and Bampara Kouyate vs Ricardo Bravo.

For Reis, the booking is the first confirmed defense of the belt he won almost a year ago. For Oliveira, it is a high-stakes ONE debut against a champion who has yet to lose under the promotion's rules.