Sergio Pettis was losing just about every second of the fight until deep into the fourth round. Kyoji Horiguchi was faster, stronger, showed better wrestling and was winning the striking battle. Pettis had absolutely no answers.

Until he did.

Pettis crushed Horiguchi with a spinning-backfist knockout at 3 minutes, 24 seconds of the fourth round Friday night in the main event of Bellator 272 at Mohegan Sun in Uncasville, California. With the victory, Pettis retained the Bellator bantamweight title and might have pulled off the best KO of 2021. It was only Pettis' fourth KO/TKO in 27 career fights.

"I came out here and got beat up for four rounds pretty much," Pettis said in his postfight interview. "I was just like, 'Man, I'm losing this fight. I've gotta do something spectacular.' It came out at the right time."

Pettis pressured Horiguchi against the cage with a combination, but Horiguchi ducked a Pettis right high kick. In the same motion, Pettis continued his spin and whipped through a backfist with his left hand. Horiguchi didn't see it coming and took it right on the chin. He was unconscious on impact.

The story coming into the fight was that Horiguchi was the former champion who never lost the belt in the cage; he had to relinquish the title in 2019 due to an ACL tear. In December 2020, Horiguchi returned from injury to win back the bantamweight title in Japan's Rizin promotion. He once held the Rizin and Bellator titles at the same time. Bellator signed Horiguchi in September, and the plan for him was to come back and regain the Bellator gold, too.

Pettis, though, had other plans. Horiguchi was dominant for most of the fight and outstruck Pettis 73-18 for the fight. He landed hard calf kicks, moved in and out expertly and mixed in takedowns with ground and pound. Pettis was searching for answers throughout, unable to hit the lightning-quick, light-on-his-feet Horiguchi. But in the fourth, Pettis was finally able to dictate the pace himself and put Horiguchi in a vulnerable position. And he capitalized on it in spectacular fashion.

Horiguchi was transported to the hospital afterward, according to Bellator officials.

Pettis (22-5) has won five straight, including a 4-0 mark in Bellator after signing as a free agent from the UFC. Pettis, a Milwaukee native and brother of former UFC lightweight champion Anthony Pettis, won the Bellator bantamweight title by beating Juan Archuleta via unanimous decision in May. Pettis, still just 28 years old, made his debut in the UFC at age 20 in 2013 and has now fully come into his own as an elite fighter.

Horiguchi (29-4), considered one of the best fighters in the world not in the UFC, stopped Kai Asakura via first-round TKO to win the Rizin bantamweight title back in December 2020. The Japan native, who lives and trains in Florida, avenged a previous knockout loss to Asakua and has now actually been knocked out in two of his last three fights. Horiguchi, 31, had won 13 straight prior to this 1-2 stretch.

Earlier on the card, Bellator announced it would be holding a bantamweight grand-prix tournament in 2021, featuring both Horiguchi and Pettis. The other participants are former champ Archuleta, Raufeon Stots, Patchy Mix, Magomed Magomedov, Leandro Higo and Conor McGregor protege James Gallagher.